chuong 3 cau truc tinh the

5/23/2018 Chuong 3 Cau Truc Tinh The

1/61

Vt liu v c

NXB i hc quc gia H Ni 2007.

Tr 67 93.

Tkho: Cu trc tinh th, cu trc tinh thca cc oxit.Ti liu trong Thvin in tH Khoa hc Tnhin c thc sdng cho mc

ch hc tp v nghin cu c nhn. Nghim cm mi hnh thc sao chp, in n phc

vcc mc ch khc nu khng c schp thun ca nh xut bn v tc gi.

Mc lc

Chng 1 CU TRC TINH TH ......................................................................................21.1 Cc phng php m tcu trc tinh th...................................................................2

1.1.1 M ttheo kiu tbo mng li.......................................................................21.1.2 M tcu trc theo kiu xp kht cc khi cu.................................................. 91.1.3 M tcu trc bng cch ni cc khi a din trong khng gian....................14

1.2 Cu trc tinh thca cc oxit v mt shp cht quan trng ................................. 151.2.1 Cu trc tinh thca mt soxit...................................................................... 161.2.2 Hp cht gia cc oxit...................................................................................... 24

1.3 Nhng nt c bit ca tinh thcng ho trv tinh thkim loi............................ 481.4 Cc yu tnh hng n kiu cu trc tinh th ..................................................... 52

1.4.1 Tnh hp thc SPT ca cc nguyn t .......................................................... 521.4.2 nh hng ca kiu lin kt ............................................................................ 531.4.3 nh hng ca bn knh nguyn t, ion .......................................................... 54

Chng 1.Cu trc tinh th

GS. Phm Vn Tng


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2

Chng 1

CU TRC TINH TH1.1 Cc phng php m tcu trc tinh th

Cu trc tinh thlin quan n mi tnh cht ca vt liu. Do tng hp c loivt liu c cc tnh cht mong mun phi hiu r cu trc bn trong ca n v t la chn

phng php chto hp l.

C nhiu cch m tcu trc tinh th: Da vo kiu tbo mng, vo cch sp xp khtkhi cu, da vo cch ni cc a din trong khng gian. Trong cc gio trnh tinh thhcu c trnh by cc phng php . y chtrnh by tm tt nhng vn lin quan nmn vt liu hc.

1.1.1 M ttheo kiu tbo mng li

Trong cht rn dng tinh th, cc tiu phn (nguyn t, ion, phn t,) c sp xp mtcch u n, tun hon to thnh mt mng li khng gian. Gista chn mt tiu phn A

bt k lm gc to, ri dng htrc toAX, AY, AZ theo 3 hng trong khng gian.Gi gc lp bi 3 trc l , , v gi khong cch u n gia cc tiu phn theo trcAX l a (thng sn vtheo trc AX), theo trc AY l b, theo trc AZ l c. Thtch b nhttrong khng gian ABCDABCD c cha mi yu ti xng c trng cho khng gian gi

l tbo mng li.

A

B

C

D

A'

B' C'

D'

X

Y

Z

a

b

Hnh 1Mng li khng gian

Ty theo cc gi tra, b, c, , , , ngi ta phn ra thnh 7 htinh thvi cc kiu mng cskhc nhau, mi mng cs li phn thnh cc kiu mng li khc nhau vc k hiu nhsau: mng csn gin k hiu l P, nu tm ca cc mt mng csccha mt tiu phn na th gi l mng li tm mt v k hiu l F, nu chtm ca hai yc cha thm tiu phn th gi l mng li tm y v k hiu l C, nu ti tm im ca mng csc cha mt tiu phn th gi l mng li tm khi v k hiu l I. Bng 1 di

y gii thiu 7 htinh thv 14 kiu tbo mng li.


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3

Bng 1.7htinh thv 14 kiu tbo mng

HCc thng st

bomngYu ti xng c

trng nht Cc kiu mng

Lp phng (cubic) a = b = c= = = 90o

4 trc bc ba P. F. I

Bn phng (tetragonal) a = b c= = = 90o

1 trc bc bn P. I

Trc thoi (orthorhombic) a b c= = =90o

3 trc bc hai P. F. I. C

Lc phng (hexagonal, trigonal) a = b c= = 90o,

= 120o

1 trc bc su P

Mt thoi (Rhombohedral) a = b = c= = 90o

1 trc bc ba P

n t (monoclinic)a b c= = 90o,90o

1 trc bc hai P. C

Tam t (triclinic) a b c 90o

khng P

Hlc phng (Hexagonal) v htam phng (Trigonal) u c thng s tbo mngnhnhau.

Ct th3 trong bng 1 cha ra yu ti xng c trng nht ca mi h. Cn syuti xng ca cc hth c rt nhiu. V dc nhiu yu ti xng nht l hlp phng.

Hlp phng c 3 trc i xng bc 4 (3A4) l cc ng thng ni tm im ca hai mti din nhau, 3 ng ny trc giao vi nhau ti tm tbo, 4 trc i xng bc ba (4A3) l

cc ng thng ni hai nh i din nhau, su trc i xng bc hai (6A2) l cc ngthng ni im gia 2 cnh i din nhau, ba mt i xng M (3M) l mt phng i qua tmim ca 4 cnh song song vi nhau, su mt i xng M (6M) l cc mt ct khi lp

phng theo tng cp ng cho mt, mt tm i xng (C). Nhvy khi lp phng ccc yu ti xng l:

3A4, 4A3,6A2, 3M, 6M, C

Cng vy cc yu t i xng ca h t phng l 1A4, 2A2, 2A2, M,2M, 2M, C.

Cc yu ti xng ca htrc thoi l A2, A2, A2, M, M, M, C.

Cc yu ti xng ca hlc phng l A6, 3A2, 3A2, M, 3M, 3M, C.Cc yu ti xng ca h mt thoi l A2, 3A2, 3M, C.

Hn t c cc yu ti xng: A2, M, C.


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4

P

ab

c

C

c

ab

I

ab

c

F

c

ab

Hnh 2Bn tbo mng li ca htrc thoi

P: l mng li n gin F: l mng li tm mt

C: l mng li tm y I: l mng li tm khi

Trong mng li tinh thc rt nhiu hmt phng song song v cch u nhau. Mi

mt hmt phng song song vi nhau c c trng bng 3 chsh k l (gi l chsMile (Miller)). xc nh chsh, k, l ca mt mt phng bt ktrong mng li tinh th,trc ht cn chn gc toO v ba trc xut pht tO l Ox, Oy, Oz. Thng sn vtheo trc Ox l a, theo Oy l b v theo Oz l c. V dmt 1 trn hnh 3 ct Ox im ng vi1/2 thng sn v(a/2), ct Oy im ng vi mt thng sn v(b/1) ct Oz im ngvi 1/3 thng sn v(c/3). Ly gi trnghch o ca cc s ta c chsh k l camt 1 l 2 1 3. C mt hcc mt phng song song v cch u mt 1 , trn hnh vc ghimt 2. Hmt phng gi l hmt 2 1 3 c mt 1 gn vi gc tonht. Hnh 4 giithiu chsMile ca mt smt phng khc nhau.

y

z

x1

2

a

b

c

0o a/2

c/3 b

Hnh 3

Xc nh chsMile hkl ca mt phng trong mng li tinh th

(a) (b) (c)

z

x

y

b

a

c Oy

z

x

a

b

c o

b

a

c

ab

x

z

y

b

a

c

O1 2

a


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Hnh 4ChsMile ca mt smt phng khc nhau: a(111); b(101); c(010)

Mt phng gch gch hnh 4a ct Ox, Oy, Oz im ng vi mt thng sn va, b,c nn gi l mt 1 1 1. Hnh 4b vmt phng ct trc Ox, Oz im ng vi mt thng s

n vv song song vi trc Oy (ct Oy ) nn gi l mt 1 0 1. Hnh 4c c cc mt vsong song vi nhau, ta chn mt xc nh chsMile ca hmt phng ny, v mti qua im gc O khng thxc nh c cc gi trh k l. Mt song song vi trc Oxv Oz ct Oy mt thng sn vb nn gi l mt 0 1 0.

Thng tin quan trng nht khi kho st mng li khng gian l gi trkhong cch giacc mt mng dhkl. Tkt qughi phnhiu xtia X cho ta bit cc gi tr ca mu nghincu, do bit c sc mt ca cc pha rn trong mu. Mi htinh thc mt mi linhgia cc gi trdhklvi cc thng sca tbo mng.

Vi hlp phng ta c:2 2 2

2 2hkl1 h k ld a+ += (1)

v thtch tbo V = a3

Vi htphng ta c:2 2 2

2 2 2hkl

1 h k l

d a c

+= + (2)

v thtch tbo

V = a2.c

Vi htrc thoi ta c:2 2 2

2 2 2 2hkl

1 h k l

d a b c= + + (3)

v thtch tbo V = a.b.c

Vi hlc phng ta c:

2 2 2

2 2 2hkl

1 4 h kh k l

3d a c

+ += +

(4)

thtch tbo

V=23.a .c

2

= 0,866a2.c

Vi hn t:

2 2 2 2

2 2 2 2 2hkl

1 1 h k .sin l 2hl cos

d sin a b c ac

= + +

(5)

thtch tbo


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V= abc.sin

Vi htam t ta c:

(2 2 2 2 2 2 2 2 2 2 2 2

2 2hkl

1 1h b c sin k a c sin l a b sin

d V= + +

(6)2 2

2

2hkabc (cos.cos.cos) 2kla bc(cos.cos.cos )

2hlab c.(cos.cos.cos))

+ +

+

Thtch tbo:

V=abc(1- cos2- cos2- cos2+ 2cos.cos.cos)1/2

Di y kho st mt vi gi trc trng ca tbo mng li kim loi. Trc ht quyc rng mng li kim loi gm cc nguyn txp kht nhau, nhng dhnh dung, trongcc hnh vchng ta biu din cc nguyn tbng nhng vng trn nh.

Mng li lp phng tm khi: thng stbo mng l a, mi tbo cha hai nguyn t,

quan hgia bn knh nguyn tv hng smng l:a 3

r4

= , t xc nh c chc c

C (compact).

=th tch ca 2 nguyn t

Cth tch t bo

=

3 3

3 3

4 4 a 32( .r ) 2( .( ) )

3 3 4 0,68a a

= =

iu c ngha l trong tbo lp phng tm khi c 32% khong trng. Mi nguyn

tc bao quanh bng 8 nguyn tkhc vi khong cch u la 3

2 , ngha l sphi tr

(SPT) bng 8, khi lng ring3

2Md

Na= (M l nguyn tlng, N l sAvgar).

T

TT

T

Hnh 5.Tbo mng lp phngtm khi

Hnh 6Vtr cc hc trng btdin (hc O), k hiu

Hnh 7Vtr cc hc trng tdin (hc T), khiu

C hai loi hc trng l hc bt din (hc O) v hc tdin (hc T).

+ Hc O:

Tm ca 6 mt u l hc O chung cho 2 tbo cnh nhau.


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im gia 12 cnh u l hc O chung cho 4 tbo cnh nhau.

Do mi tbo c: (6 1/2) + (12 1/4) = 6 hc O (hnh 6).

+ Hc T: Mi mt c 4 hc T chung cho 2 tbo cnh nhau. Do mi tbo c (4 6

1/2) = 12 hc T (hnh 7).Mng li lp phng mt tm: Thng stbo mng l a. Mi tbo cha 4 nguyn t.

Quan hgia bn knh nguyn tv cnh l:a 2

r4

= , c chc

=th tch ca 4 nguyn t

Cth tch t bo

=

3 3

3 3

4 4 a 24( .r ) 2( .( ) )

3 3 4 0,74a a

= =

Mi nguyn tc bao quanh bng 12 nguyn tkhc vi khong cch bnga 2

2,

SPT =12, khi lng ring3

4MdNa

= .

Hnh 8Mng li lp phng tm mt

Hnh 9Vtr hc O, k hiu

Hnh 10.Vtr cc hc O, k hiu x

Trong tbo lp phng mt tm c 26% khong trng l cc hc O v hc T.

+ Hc O:

Tm tbo c 1 hc O (hnh 9).


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Gia cc cnh u c hc O chung cho 4 tbo (hnh 10).

Vy mi tbo c 1 + 12 1/4 = 4 hc O.

+ Hc T: Mi tbo c 8 hc T nm trong tbo cc to: (1/4, 1/4, 1/4); (3/4, 1/4,

1/4); (3/4, 3/4, 1/4); (1/4, 3/4, 1/4); (1/4, 1/4, 3/4); (3/4, 1/4, 3/4); (3/4, 3/4, 3/4); (1/4, 3/4, 3/4)(hnh 11).

Mng li lc phng: Thng stbo mng l a, c (hnh 12). Mi tbo c 2 nguyn

t. Quan hgia bn knh nguyn tv thng stbo la

r2

= .

chc c =Th tch 2 nguyn t

CTh tch t bo

Thtch 2 nguyn t3

1

4 aV 2

3 2

=

; Thtch tbo V2 = abc

a

c

aA1

B1 C1

D1

A

B

CD

(a)

A B

CD

A1B1

D1 C1

60o

120o

(b)

Hnh 11Vtr cc hc T

Hnh 12Khi gm 3 tbo (a), tbo mng li lc phng (b)

T

5C

8

8

3C

Hnh 13Vtr cc hc T (k hiu )

T

T

T

T

T

T

T

T


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Hnh 14Vtr cc hc O (k hiu)

a 3b ;

2=

2

2

a 3V c;

2= mt khc

a 3;

c 2 2=

Do C 0,743 2

= =

SPT =12; Khi lng ring2

4Md

Na 3c=

Mi tbo c 2 hc O v 4 hc T (hnh 13 v 14).

1.1.2 M tcu trc theo kiu xp kht cc khi cu

Theo nguyn l xp kht, th khi khng c snh hng ca lin kt, cc tiu phn tothnh tinh thc khuynh hng sp xp sao cho khong khng gian tdo c thtch b nht,ngha l c chc c ln nht. Nu cc tiu phn to thnh tinh thu c dng qucu ving knh bng nhau th c 2 kiu xp kht gi l xp kht lc phng (kiu ABABA) vxp kht lp phng (kiu ABCABCAB). Hnh 15 trnh by cch xp kht ca mt lp qucu . Trong lp xp kht ny (gi l lp A) mi mt qucu (v dqua cu K) c baoquanh bng 6 qucu khc. Trong hnh b, mi qucu chtip xc vi 4 qucu khc, ykhng phi l mt xp kht. Trong lp xp kht c 3 hng xp kht (XX, YY, ZZ) (hnh15a), hnh 15b chc 2 hng xp kht. Trong mt xp kht ny c cc dy ltrng R v

dy ltrng P.


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RP

1

2

34

5

6

P

y y'

x

x'z

z'

(a)

pppR R

K

(b) Hnh 15Mt phng gm cc qucu xp kht nht (a), cch xp khng kht (b)

By gichng ta t lp xp kht th2 (gi l lp B) ln trn lp A. Mun cho khng

gian tdo c thtch b nht th phi t sao cho cc qucu ca lp B nm ng vtr lmgia 3 qucu ca lp A v ngc li, cc qucu ca lp A phi nm ng cc vtr lmca lp B. Mun vy th cc qucu ca lp B hoc l phi nm vo tt ccc vtr P, hocl phi nm vo tt ccc vtr R ca lp A (xem hnh 15). Ta c 2 lp xp kht (hnh 16).

t lp th3 ln lp th2 ta c 2 cch. Nu t sao cho cc qucu ca lp th3nm vo vtr S ca lp th2 (hnh 16) th tt ccc qucu ca lp 3 u trng vo vtrtng ng ca lp thnht. Ngha l chu k lp li ca cc lp l 2, cc lp xp theo thtABABA. Kiu xp kht nhvy gi l xp kht lc phng.

A

B

TTT

SS S

S S

T T TT

Hnh 16Hai lp xp kht A v B

A

B

C


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Hnh 17Ba lp xp kht ABC to thnh kiu xp kht lp phng

Nu t lp th3 sao cho cc qucu nm lt vo vtr T (xem hnh 16) th shnh thnhmt lp mi (lp C), n lp th4 mi lp li chu k tc l lp A. Cch xp nhvy gi l

xp kht lp phng v thtlin tc ca cc lp l ABCABCAB (hnh 17). Xp kht lpphng v xp kht lc phng l hai kiu cu trc n gin v quan trng nht. Ngoi racng cn c nhiu kiu xp kht vi th t cc lp phc tp hn, v dABCACB... hocABAC to thnh nhng chu k lp li ln hn (xem cu trc tinh thca -Al2O3 - hnh29).

Trong 2 kiu xp kht lc phng v xp kht lp phng, mi qucu u tip xc vi12 qucu khc (SPT = 12).

chc c ca c2 kiu xp kht ny u bng nhau v bng 0,74. iu ny c ngha ltrong chai kiu xp kht nht vn cn 26% thtch l cc khong trng. C hai loi hctrng gi l hc trng tdin (hc T) v hc trng bt din (hc O). Hc T l khong khng

gian gia 4 khi cu xp kht vo nhau. Tuthuc vo khi cu nh ca tdin nm trnhoc di m phn thnh hc T+ hoc T(hnh 18). Hc O l khong khng gian nm gia6 qucu xp kht ca 2 lp st nhau, su qucu gm 4 qucng nm trn mt mt phngv 2 qunm vhai pha ca mt phng .

1

2 3

45

6

(a) (b) (c)

Hnh 18Cc hc trng trong mng li xp kht nht Hc T+ (a), Hc T- (b), Hc O (c)

Vic chn mt phng cha 4 qu cu c th ly tdo theo nhiu cch. V d, cc qu1264 hoc 2345 hoc 1356. Hnh 19 trnh by cc hc trng gia 2 lp xp kht. Mng tinhthca cc oxit gm cc ion O2xp kht, cn cc cation c phn bvo cc hc T v O.V rng trng tm ca tdin gn y hn nh nn cation hc T khng ng vo v trchnh gia 2 lp, cn cation hc O th nm ng chnh gia 2 lp. Cc cation khi chui vohc T v O slm gin nphn mng oxi.

Hc t din T-

Hc t din T+

Hc bt din O

Hnh 19

Sphn bcc hc trng gia hai lp xp kht (lp cu pha trn vvng


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m, lp cu pha di vng chm chm)

Tbo mng ca kiu gi ghm chc c lp phng (hay cn gi l lp phng tmmt) c trnh by trn hnh 20a, cn hnh 21 trnh by tbo mng ca kiu gi ghm chcc lc phng.


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12

3

4

5

6

7

2

3

4

5

6

7

(a) (b)

Hnh 20Tbo mng lp phng tm mt c to thnh tkiu gi ghm cc qucu theo kiu chc c lp phng

Kiu gi ghm chc c lp phng trng vi kiu tbo lp phng mt tm (hnh 20a).Ni chung iu ny khng ddng thy c, v rng cc mt ca tbo lp phng khngtrng vi lp xp kht, trong mi qucu chtip xc vi 4 qucu khc chkhng phi 6qu. Trong tbo lp phng mt tm th lp xp kht l cc mt song song vi mt phng111. thy c r hn, ta bi qucu vtr 1 ca hnh 20a th thy ngay lp di gmcc qucu 2, 3, 4, 5, 6, 7 (hnh 20b) nm trn cng mt mt phng (song song vi mt 111).T ta c thkt lun rng cu trc gi ghm chc c lp phng c 4 mt xp kht trcgiao vi ng cho ca khi lp phng.

Tbo mng kiu lc phng trng vi kiu gi ghm chc c lc phng, iu ny dthy c trn hnh 21, y cc mt csca mng u trng vi mt xp kht.

60o120o

a

c

a

a

Hnh 21Tbo mng lc phng c to thnh tsgi ghm chc c lc phngcc khi cu

a s cc kim loi u kt tinh theo mt trong ba kiu lp phng tm mt(ABCABC), lc phng (ABAB) v lp phng tm khi. Bng 2 cho bit kiu tbo,thng stbo ca mt skim loi.


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Bng 2Cu trc v thng stbo mng li ca mt skim loiLp phng tm mt

(kiu ABCABC)Lc phng (kiu ABAB) Lp phng tm khi

Kim loi a () Kim loi a () c () Kim loi a ()Cu 3,6150 Be 2,2859 3,5843 Fe 2,8664

Ag 4,0862 Mg 3,2095 5,2104 Cr 2,8839

Au 4,0786 Zn 2,6650 4,9470 Mo 3,1472

Al 4,0494 Cd 2,9793 5,6181 W 3,1648

Ni 3,5238 Ti 2,9500 4,6860 Ta 3,3058

Pd 3,8898 Zr 3,2320 5,1470 Ba 5,0250

Pt 3,9231 Ru 2,7058 4,2819

Pb 4,9506 Os 2,7341 4,3197

Re 2,7600 4,4580

Vic mt kim loi no kt tinh theo kiu mng li ny hay mng li khc l mtvn cho n nay vn cha r. Trong hai kiu cu trc lp phng tm mt v lc

phng u c chc c ln (C = 0,74) cn chc c ca kiu lp phng tm khi nhhn (C = 0,68). Kt qutnh ton cho thy nng lng mng li ca cc kim loi c cu trclc phng v lp phng tm mt gn tng tnhau, do skhc nhau vcu trc c thdo skhc nhau vcu trc vng ca chng.

C mt skim loi c bin ho th hnh, ngha l c thc cc kiu cu trc khc nhau.V d st, tu thuc vo nhit c th c cu trc lp phng tm khi (Fe-) hoc lp

phng tm mt (Fe-); coban ngoi kiu cu trc lp phng tm mt v lc phng li cnc th to ra cc dng khc vi chu k lp li ca cc lp xp kht phc tp hn. y ltrng hp ng vi dng a hnh c bit (polytypism) khi m skhc nhau vcu trc canhng dng th hnh chxy ra theo mt hng. Trong cc kim loi c cu trc gi ghmchc c ca tt ccc lp nguyn tkch thc ging nhau, cn skhc nhau vcu trc chl cch sp xp ln nhau ca cc lp . Tuy rng chc hai cch chnh sp xp cc lp lABC (lp phng tm mt) v AB (lc phng) nhng cng c thhnh thnh rt nhiu kiusp xp lun phin phc tp hn. l trng hp ca coban kim loi. C nhng vt liutrong c dng th hnh vi chu k lp li gia cc lp xp kht ti vi trm lp nguyn t.Shnh thnh nhng cu trc nhvy ang l vn cha gii thch c. V dnhc kiu

cu trc vi chu k lp li ti vi trm lp, dy ti 500. Cng c quan im cho rng chuk lp li ln nhvy lin quan vi cchxon c khi tinh thln dn sinh ra bin vxon.

1.1.3 M tcu trc bng cch ni cc khi a din trong khng gian

V dtinh thmui n (NaCl) c thm tbng cch ni cc khi bt din [NaCl6]5qua

mt cnh chung (hnh 22), mng tinh thnhvy c trnh by hnh 23.

Tuy nhin khng phi ton khi khng gian c lp y bng cc bt din, m vn cnli cc khong trng, i vi tinh thNaCl th l cc khong trng tdin nhtrn hnh23.

Kiu m tnhvy rt thun li cho cch trnh by mng tinh thca silicat. V dmngtinh th SiO2 c trnh by bng cch ni cc t din [SiO4]4 qua nh, mng tinh th


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khong vt st c trnh by theo cch ni cc tdin [SiO4]4vi cc bt din [Al(OH)6]

3

qua nh, mng tinh thzeolit c m ttheo cch ni cc bt din ct [Si24xAlxO48]x+qua

cc mt bn (xem phn silicat). V cc a din u c cation nm tm, anion cc nh, nnni cc a din qua nh, cnh hoc cc mt chung th phi lu n lc y gia cc cation,

c bit l cc cation c kch thc b v in tch ln, v dnhSi4+. Tt nhin mng libn nu cch ni sao cho lc y ny b nht, ngha l khong cch gia cc cation xa nht.Hnh 24 v bng 3 cho thy khong cch gia cc cation gim dn khi ni cc a din quanh, cnh, mt.

Hnh 22Tbo mng NaCl c hnh thnh theocch ni cc bt din theo cnh chung

Hnh 23Mng tinh thNaCl c xy dng theo cchni cc bt din [NaCl6]

5 qua cnh chung

o

(a)

o

o

o

o

oo

oo o

MM

X

(b)

MM

X

90o

X

MM

X

71o

(c)

X

M M = 2MX(M - O, X - o) M - M=

2 MX = 1,411MX M - M = o2(1 cos71 )MX = 1,16M

Hnh 24Khong cch cation-cation khi ni cc bt din qua nh (a); qua cnh (b) v khi ni cc tdinqua cnh (c)

Khong cch M-M khi ni 2 a dina din

Bng nh Bng cnh Bng mtHai tdin 2MX 1,16MX 0,67MXHai bt din 2MX 1,41MX 1,16MXBng 3Khong cch gia cc tm a din cnh nhau MX4v MX6

1.2 Cu trc tinh thca cc oxit v mt shp cht quan trng

st vi i tng nghin cu vt liu v c, trong phn m tcu trc tinh thdiy strnh by loi hp cht in hnh nht l oxit v hp cht gia cc oxit nhM2O, MO,M2O3, MO2, AB2O4, ABO3, AB2O7,... v silicat. Cc hp cht v ckhc (halogenua, sunfua,nitrua,) sc ni n khi c cu trc tng tvi oxit.


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1.2.1 Cu trc tinh thca mt soxit

1.2.1.1 Oxit c cng thc chung MO

Na+ Cl

Hnh 25Tbo mng li kiu NaCl

Oxit kim loi ho tr2 nu c tlrM2+/rO2nm trong khong 0,414 n 0,732 v c linkt ch yu l lin kt ion th c mng li tinh th thuc kiu NaCl. Ta c thbiu dinmng li tinh thny theo c3 phng php trn. y biu din tbo mng. C thxemtbo mng ca loi ny gm hai phn mng lp phng mt tm ca cation M2+ v caanion O2lng vo nhau mt khong bng 1/2 cnh ca lp phng. Mi tbo gm 4 phn

tMO, SPT ca cation v anion u bng nhau v bng 6.Bng 4Mt shp cht cu trc theo kiu NaClHp cht a () Hp cht a () Hp cht a ()

MgO 4,2130 MgS 5,2000 MgSe 5,462CaO 4,8105 CaS 5,6948 CaSe 5,924SrO 5,1600 SrS 6,0200 SrSe 6,246BaO 5,5390 BaS 6,3860 BaSe 6,600TiO 4,1770 MnS 5,2240 CaTe 6,660MnO 4,4450 SnAs 5,7248 BaTe 7,000FeO 4,3070 TiC 4 ,3285 UC 4,955CoO 4,2600 LaN 5,3000 ScN 4,440NiO 4,1769 TiN 4 ,2400 UN 4,890

CdO 4,6653

Hp cht c tlrcation/ranionnm gia 0,225 v 0,414 v lin kt chyu l ion th c cutrc kiu ZnS.

ZnS c hai dng th hnh l blend (hoc cn c tn l sphalerit) v vuazit.

Blend c tbo tinh th lp phng tm mt ca S2, ion Zn2+nm 4 trong 8 hc tdin ca phn mng lp phng tm mt S2 (hnh 26). Toca Zn2+l: 1/4, 1/4, 1/4;3/4, 3/4, 1/4; 3/4, 1/4, 3/4 v 1/4, 3/4, 3/4. Hng smng ca blend a = 5,43; d = 4,092.Bng 5 gii thiu cc hp cht c cu trc kiu blend.


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Zn

S

Hnh 26Tbo mng ca blend (ZnS)

Bng 5

Mt shp cht cu trc kiu blend

Hpcht a ()Hp

chta ()

Hp

chta ()

Hp

chta ()

Hp

chta ()

CuF 4,255 BeS 4,8624 -CdS 5,818 BN 3,616 GaP 5,448

CuCl 5,416 BeSe 5,070 CdSe 6,077 BP 4,538 GaAs 5,653

-CuBr 5,690 BeTe 5,54 CdTe 6,481 BAs 4,777 GaSb 6,095

-CuI 6,051 -ZnS 5,406 HgS 5,852 AlP 5,451 InP 5,869

-AgI 6,495 ZnSe 5,667 HgSe 6,085 AlAs 5,662 InAs 6,058

-MnS 5,600 ZnTe 6,102 HgTe 6,453 AlSb 6,135 InSb 6,478

-MnSe 5,880 SiC 4,358

Khi un nng ti 1020oC th blend chuyn thnh vuazit. Tbo mng ca vuazit c phnmng S2gi ghm chc c lc phng (hnh 27). Cc ion Zn2+chim ht tt chc tdin

T+, cn cc hc tdin Tv hc bt din O u trng.

Hnh 27 trnh by mt tbo mng ca vuazit. C thhnh dung tbo mng ny gmhai phn mng xp kht lc phng cation v anion lng vo nhau mt khong bng 3/8 chiucao. Trong thc thai phn mng ny lng vo nhau khng ng vi gi tr3/8 (0,375) chiucao, m tutheo tng loi cation gi trdch chuyn khc nhau (gi tru trong bng 6).

Hng smng ca vuazit a = 3,811; c = 6,234; d = 3,98 4,08.

Mt trong nhng tnh cht c trng ca phn mng xp kht lc phng l gi trc/a.Trng hp l tng th ts bng 1,633. Cc gi tr trn bng 6 u khc vi 1,633,iu ny chng trng cc mt khng hon ton xp kht.


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18

60 o120 o

a

c

38

c

60 o

38

c

a

c

120 o

Hnh 27Tbo mng kiu vuazit

Bng 6

Gii thiu mt shp cht c cu trc vuazi

Cht a () c () u c/a Cht a () c () u c/aZnO 3,2495 5,2069 0,345 1,602 MnS 3,976 6,432 1,618

ZnS 3,8110 6,2340 1,636 MnSe 4,120 6,720 1,631

ZnSe 3,9800 6,5300 1,641 AlN 3,111 4,978 0,385 1,600

ZnTe 4,2700 6,9900 1,637 GaN 3,180 5,166 1,625

BeO 2,6980 4,3800 0,378 1,623 InN 3,533 5,693 1,611

CdS 4,1348 6,7490 1,632 TaN 3,050 4,940 1,620

1.2.1.2 Oxit c cng thc M2O3

l cc oxit Al2O3 (corun), Fe2O3 (hmatit), Cr2O3, Ga2O3, Ti2B3, Al2O3 c nhiu

dng th hnh. iu ny cng dhiu v tlrAl3+/rO2= 0,42 tc l nm gia hai sphi tr l4 v 6. Trong cc dng th hnh chc 3 dng quan trng l , , .

Al2O3l dng th hnh bn vng nht, loi ny cn c tn l corun, tinh thcorun gmphn mng xp kht lc phng ca ion oxi. Cation Al3+chim 2/3 hc bt din, cn hc T+

v T u btrng.

O2-

Al3+

O2-

Al3+

Hnh 28Cu trc tinh thcorun Al2O3

Khong cch gia hai lp xp kht oxi bng 2,16. Tbo nguyn tca corun thuc hmt thoi, chiu di cnh bng 5,12, gc nhn gia cc cnh bng 5o17. Tbo nguyn tc

4 ion nhm v 6 ion oxi. Cc oxit c cu to ging corun gm hmatit Fe2O3, Cr2O3, Ga2O3,Ti2O3.


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-Al2O3. Tn gi Al2O3chmt nhm hp cht c cng thc M2O.nX2O3. Gi trca n thay i t8 n 11. M l cation ho tr+1 nhCu+, Ga+, Tl+, In+, NH4

+, H3O+, X l cc

cation Al3+, Ga3+, Fe3+. Quan trng nht trong cc loi hp cht ny l natri -Al2O3 (M lNa+, X l Al3+) c bit t lu nh l mt sn phm phkhi sn xut thu tinh. Natri

-Al2O3 c hnh thnh trong ni thutinh khi tng tc gia Na2O c trong khi nng chyvi Al2O3trong thnh phn gch chu la. Tn gi -Al2O3rt dlm ngi ta nhm ln vimt dng th hnh ca tinh thAl2O3, nhng do thi quen dng tlu nn by gikhngthay i na. Thc ra vai tr Na2O nhl mt tc nhn n nh cu trc tinh thca loi hpcht ny. Hnh 29 trnh by mng anion trong -Al2O3. Trn hnh ny cho thy c4 lp oxigi ghm chc c li c mt lp chc 1/4 ion O2cn 3/4 vtr O2trng. Cc ion Na+c phn btrong lp thiu oxi . Do bn knh ion O2rt ln hn bn knh ca Na+, mtkhc lp ny rt rng nn Na+chuyn ng kh ddng theo mt phng ca lp ny.

C

B

A

Sp

Sp

Sp

c

AC

C

BAC

AB

C

AB

BA

Hnh 29Cc lp oxi xp kht trong -Al2O3

Mng tinh th-Al2O3cha cc bloc tng tspinen (Sp). Bloc Sp gm 4 lp oxi gighm chc c lun phin theo th tABCA c trng ca cu trc lp phng. Ion Al3+chim mt svtr tdin v bt din gia hai lp oxi. Cc bloc Sp tch bit nhau bng mt

lp thiu oxi, ion Na+

nh v trong lp thiu oxi . Tbo mng li lc phng c ccthng sa = 5,60, c = 22,50. Cc lp oxi trc giao vi trc c. Tbo ca -Al2O3c cha2 bloc Sp. Cu trc spinen y c xem nhcu trc MgAl2O4cha khuyt tt (xem hnh35). Trong spinen MgAl2O4c tlion Mg

2+v Al3+l 1 : 2 trong khi spinen ca -Al2O3chc Al3+(khng kn cc ion hp kim ho nhLi+, Na+), do cn bng in tchtrong cc bloc spinen phi c cha cc ltrng Al3+.

Tinh thca cc oxit t him c mc oxi ho +3 thng dng trong vt liu gm c cutrc khc vi cu trc corun v bn knh Ln3+ln hn bn knh ca Al3+. Theo Holsmit, c th

phn thnh 3 loi oxit t him: loi A c cu trc mt thoi hoc lc phng, loi B thuc hn t, loi C thuc hlp phng. Oxit t him cng c nhiu dng th hnh.


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Bng 7

Tnh cht ca cc dng th hnh ca Al2O3

Chskhc

xDng th

hnh

Htinh

th

DngD

(g/cm3

) ng np

Bin ho khi

nung

-Al2O3

(corun)lc phng

Bn, mt

thoi3,99 1,786 1,76

2050oC nng

chy

-Al2O3 lc phng 3,33,4 1,680 1,651600oC thnh

-Al2O3lp

phngBt din 3,6

1200oC thnh

Loi A (kiu La2O3) c La2O3, Ce2O3, Pr2O3.

Loi B c Ge2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Cd2O3, Lu2O3, Tb2O3, Dy2O3(trn 2000oC).

Loi C (kiu Tl2O3 hoc Mn2O3) c: Sm2O3, Eu2O3, Cd2O3, Lu2O3, Tb2O3,Dy2O3, Ho2O3, Er2O3, Tu2O3, Yb2O3.

Cc oxit Sc2O3, Y2O3, In2O3v Tl2O3cng c cu trc loi C nhoxit t him (thuc hlp phng, mi tbo c 16 phn t).

1.2.1.3 Oxit c cng thc MO2

Tuthuc vo tlrcation/ranionhp cht loi ny c 3 kiu cu trc l kiu florit (CaF2),kiu rutin (TiO2) v kiu oxit silic (SiO2).

Kiu florit: Cc anion chim hc t din trong phn mng lp phng mt tm cacation. Hay c thhnh dung khi phn chia mang c s lp phng mt tm ca cationthnh 8 khi lp phng b bng nhau th cc anion nm tm ca 8 khi lp phng b .SPT ca cation bng 8 cn ca anion bng 4. Mi tbo c 4 phn tAB2.

Oxit, sunfua, selenua kim loi ho trmt c cu trc kiu antiflorit, ngha l vn gingkiu florit CaF2nhng y vtrca ion canxi li do ion oxi chim, cn vtr ca ion flo thcation kim loi kim chim.

(a)Ca F

(b)

TiO

(c)

SiO


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Hnh 30Tbo ca cc hp cht c cng thc AB2a) kiu florit, b) kiu rutin, c) kiu silic oxit (cristobalit)

Bng 8

Cc hp cht c cu trc florit v antiflorit

florit antiflorit

Hp

cht

a () Hp

cht

a () Hp

cht

a () Hp

cht

a ()

CaF2 5,4626 PbO2 5,3490 Li2O 4,6114 K2O 6,449

SrF2 5,8000 CeO2 5,4110 Li2S 5,7100 K2S 7,406

SrCl2 6,9767 PrO2 5,3920 Li2Se 6,0020 K2Se 7,962

BaF2 6,2001 ThO2 5,6000 Li2Te 6,5170 K2Te 8,168

BaCl2 7,3110 UO2 5,3720 Na2O 5,5550 Rb2O 6,740

CdF2 5,3895 NpO2 5,4334 Na2S 6,5390 Rb2S 7,650HgF2 5,5373 PuO2 5,3860 Na2Se 6,823

Kiu rutin TiO2: T bo mng li thuc h t phng khi tm ca cation Ti4+ cn

anion to thnh bt din u bao quanh titan (2 ion oxi nm mt trn dc theo mt ngcho, 2 ion oxi nm mt di cng theo hng ng cho , 2 ion oxi na nm ngaytrong tbo nhng theo hng ng cho khc). Mi tbo mng c 2 phn tTiO2. S

phi tr ca titan bng 6, cn ca oxi bng 3. Toca Ti l (0 0 0), (1/2 1/2 1/2) ca oxi l(x x 0), ( x x 0), (1/2+x, 1/2-x, 1/2), (1/2-x, 1/2+x, 1/2). Kt quthc nghim xc nh c x= 0,3 (xem hnh 30b v 31).

Bng 9

Mt shp cht c cu trc tinh thkiu rutin

Cht a () c () x Cht a () c () x

TiO2 4,5937 2,9581 0,305 SnO2 4,7373 3,1864 0,307

CrO2 4,4100 2,9100 TaO2 4,7090 3,0650

GeO2 4,3950 2,8590 0,307 WO2 4,8600 2,7700

IrO2 4,4900 3,1400 CoF2 4,6951 3,1796 0,306

-

MnO2

4,3960 2,8710 0,302 FeF2 4,6966 3,3091 0,300

MoO2 4,8600 2,7900 MgF2 4,6230 3,0520 0,303NbO2 4,7700 2,9600 MnF2 4,8734 3,3099 0,305

OsO2 4,5100 3,1900 NiF2 4,6506 3,0836 0,302

PbO2 4,9460 3,3790 PbF2 4,9310 3,3670

RuO2 4,5100 3,1100 ZnF2 4,7034 3,1335 0,303

C thm t cu trc mng tinh th rutin theo kiu xp kht nhhnh 31. Phn mnganion oxi xp kht theo kiu lc phng (ABAB). Cation titan chim 1/2 shc bt din theotrt t: cmt dy hc bt din btrng n mt dy hc bt din bchim ht. Trt tnythay i lun phin theo 1/2 n vca c.

Kiu silic oxit


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Silic oxit (SiO2) c nhiu dng th hnh, y ni v mt trong cc dng gi lcristobalit (hnh 30c). Cristobalit thuc hlp phng. Nguyn tSi chim cc nh, tm ccmt v 4 trong 8 hc tdin theo hai hng ng cho khc nhau (hoc c thhnh dungchia khi hnh lp phng thnh 8 khi lp phng nhbng nhau th Si l tm ca 4 khi lp

phng nh). Oxi l cu ni gia cc nguyn tsilic. Mi tbo c 8 phn tSiO2. Sphi tr ca Si bng 4, ca oxi bng 2.

Ngoi cristobalit ra SiO2 cn rt nhiu dng hnh th khc na l: thch anh, tridimit,cristobalit.

Mi dng chnh nhvy cn tn ti di nhiu dng ph.

Cc dng n tinh: cancedoan, m no, jat (ngc).

Dng v nh hnh: thutinh thch anh, opal.

b

a

(b)

Tocc nguyn t

Ti4+ 0, 0, 0 - 0.5, 0.5, 0.5

O2- 0, 0.3, 0.3 - 0, 0.7, 0.70.8, 0.2, 0.5 - 0.2, 0.8, 0.5

a

c

(a)

Hnh31a) Cu trc rutin biu din theo mt phng xp kht ca ion oxib) Hnh chiu ca tbo mng rutin trn mt y

m tcu trc ca cc dng SiO2th tt nht l dng phng php ghp cc tdinvi nhau qua nh oxi chung (hnh 32). im khc nhau ca 3 dng tinh thchnh (thch anh,tridimit, cristobalit) l vtr tng i ca 2 tdin SiO4

4(hnh 33).

thch anh ta c gc lin kt Si-O-Si bng 150o, tridimit, v cristobalit th gc lin

kt Si-O-Si bng 180

o

. Tthch anh bin thnh cristobalit chcn nn thng gc Si-O-Si t150othnh 180o, trong khi chuyn thnh tridimit th ngoi vic nn thng gc ny cnphi xoay tdin SiO4

4quanh trc i xng mt gc bng 180o


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T+

T- T+

T+

T+

T-

T-

T-

Hnh 32Cch ghp cc tdin SiO4(Si

4+, O2-)

(a)

AB

C

A'

B'C'

D )150o

A

B

C

A'

B'

C'

D

(b) (c)

A

B

C

A'

B'

C'

D

Hnh 33Sthp hai tdin SiO4a) Thch anh; b) Cristobalit ; c) Tridimit

Skhc nhau ca cc dng th hnh thcp , , chdo mc khc nhau ca gc linkt Si-O-Si .

Qu trnh chuyn ho ca cc dng th hnh -thch anh -tridimit -cristobalit

u l qu trnh c bin, cn qu trnh chuyn ho cc dng th hnh thcp ul qu trnh hbin.


24/61

24

tridimit

t

tridimit

ridimit

Thchanh

Thchanh

cristobalit

cristobalit Nngchy

163oC

117oC

573oC 253oC

870oC 1728

o C1470o C

1050o C

Hnh 34Sbiu din schuyn ho gia cc dng th hnh ca SiO2

Trong thc tnhit chuyn ho cc dng th hnh ca SiO2cn phthuc vo nhiuyu tnhsc mt ca nhiu cht khong ho, chnng nhit v.v Trn y chnuln cc dng th hnh ca SiO2p sut kh quyn. Di p sut cao cn c cc dng th

hnh khc na (xem gin trng thi ca SiO2hnh 92 v bng 30).

1.2.2 Hp cht gia cc oxit

1.2.2.1 Spinen

Spinen l tn gi khong vt c cng thc MgAl2O4. C thxem spinen nh l hp chtca hai oxit: oxit bazca kim loi ho tr2 v oxit lng tnh ca kim loi ha tr3.

MgO + Al2O3= MgAl2O4

Spinen l i din cho mt lot cc hp cht c cng thc tng qut AB2O4. Trong Al cation ho tr2 v B l cation ho tr3. Mng li spinen gm cc ion oxi gi ghm chcc lp phng mt tm, cc cation A2+v B3+ c sp xp vo cc hc tdin v bt din(T+, T, O). Mi tbo mng gm 8 phn tAB2O4, ngha l c 8 khi lp phng b (hnh35) trong c 32 ion oxi, 8 cation A2+v 16 cation B3+. Ta c thtnh ton scation, sanion v shc tdin T, shc bt din O khi tng tng ghp 8 khi lp phng tm mtli vi nhau.

Hnh 35Tbo mng ca spinen

Sion oxi gm:


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8 nh ca lp phng ln: 8 1/8 = 1

6 mt lp phng ln : 6 1/2 = 3

12 mt nhtrong lp phng: 12 1 = 12 Tng sc 32 oxi

24 mt nhpha ngoi : 24 1/2 = 12

12 cnh ca lp phng ln: 12 1/4 = 3

Tm ca lp phng ln = 1

Shc T (cn gi l phn mng A). Mi lp phng nhc 8 hc tdin nm trong lpphng . Tbo mng spinen c 8 lp phng nh. Nhvy mi tbo spinen c 8 8 =64 hc T.

Shc O (cn gi l phn mng B) gm:

8 tm ca 8 lp phng b: 8 1 = 8

24 cnh bin ca lp phng b: 24 1/4 = 6

24 cnh gia ca 6 mt bin: 24 1/2 = 12

6 cnh nm trong lp phng: 6 1 = 6

Nhvy, mi tinh thspinen c 64 + 32 = 96 hc T v O. M scation chc 8 + 16 =24 cation. Ngha l ch1/4 shc trng cha cation, cn 3/4 hc trng khng.

Nu 8 cation A nm trong 8 hc trng T, cn 16 cation B nm vo hc O th gi l mngli spinen thun, k hiu A[BB]O4.

Nu 8 cation A nm trong 8 hc trng O, cn 16 cation B phn lm hai: 8 cation nm vo

hc T, 8 cation nm vo hc O th gi l spinen nghch o, k hiu B[A.B]O4.

Nu 24 cation A v B c phn bmt cch thng k vo cc hc T v hc O th gi lspinen trung gian.

- -

3 2 2 31 x x 41 x 1 x

B A OA B+ + + +

+ vi 0 < x


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a l hng smng li spinen (), rAv rBl bn knh khi cu nm trong khng gian tdin v khng gian bt din, rOl bn knh oxi.

Stinh thkt tinh theo mng li spinen kh phbin trong hp cht v c. Trong cngthc tng qut AB2O4th A

2+c thl Cu, Be, Mg, Ca, Sr, Ba, Zn, Cd, Mn, Pb, Fe, Co, Ni.Cation B3+c thl Al, Cr, Fe, Mn, t khi gp Ga, In, La, V, Sb, Rh. Thp cc cation licho thy c rt nhiu hp cht spinen. Tuy nhin cng cn phi ni thm rng khng phi ttccc hp cht c cng thc AB2O4u kt tinh theo hlp phng nhspinen. V dnhBeAl2O4, CaCr2O4thuc hhnh thoi, cn SrAl2O4thuc htphng. Trong khi mt shp cht oxit ng vi cng thc A2BO4(ng vi A

2+, B4+), v dMg2TiO4li kt tinh theo hlp phng v c sp xp vo nhm spinen. l cc hp cht nh titanat, stanat cacoban, st(II), magi, km, Ngoi cc oxit phc tp ra, cn c cc spinen c anion lchalcogen (S2, Se2, Te2) hoc halogen. V dLi2NiF4.

Do khnng thay thng hnh, ng ho trhoc khng ng ho trcc cation trongspinen oxit lm cho slng hp cht spinen tng ln rt ln.

V dthp cc cation trong spinen oxit cho ta cc loi sau:

Spinen MgAl2O4 Mg2TiO4 LiAlTiO4 Li0,5Al2,5O4 LiNiVO4 Na2WO4

Thp cation 2;3 2;4 1;3;4 1;3 1;2;5 1;6

Cc hp cht spinen c gi trrt ln trong kthut. Chng c sdng lm bt mu,vt liu chu la, vt liu k thut in t, qu, Do vn nghin cu tng hpspinen v cc tnh cht, c, in ca chng l i tng nghin cu ca nhiu nh khoa hc.Theo dn in, c thnh gi c cu to bn trong ca spinen. V dFe3O4v Mn3O4u c cu trc spinen, nhng trong khi Mn3O4l cht in mi (khng dn in) cn Fe3O4li c dn in cao nh kim loi. l do Fe3O4 c cu trc spinen o:

Fe3+

T[Fe2+

Fe3+

]OO4, cn Mn3O4c cu trc spinen thun: Mn2+

T[Mn23+

]OO4. Trong mng tinhthspinen Fe3O4, cc ion Fe2+v Fe3+c phn btrong cc bt din. Cc bt din ny tip

xc vi nhau theo mt cnh chung, do cation st c mc oxi ho khc nhau m gn nhaunn trao i in tch ddng, ltrng dng c thchuyn tFe2+sang Fe3+. Cn mng tinhthspinen Mn3O4th Mn

3+nm trong bt din, Mn2+nm trong tdin. Bt din v tdinchtip xc vi nhau qua nh, ngha l cc cation Mn3+v Mn2+nm cch xa nhau hn sovi khong cch Fe2+ v Fe3+ trong Fe3O4. iu ny lm cho s trao i in tch trongMn3O4kh khn hn nhiu.

Bng 10

Tnh cht ca mt sspinen

Cng thc Tinh th a () cng d (g/cm3) tonc Gin n(-105)

R(900oC)

MgAl2O4 Lp

phng

(8,09) 8 3,57 2135 0,593 75,3.104

ZnAl2O4 -nt- (8,09) 7,5-8 4,58 1930 0,596 18,6.104

CoAl2O4 -nt- (8,1) >7 4,37 1960 - 11,7.104

NiAl2O4 -nt- (8,04) - 4,45 2020 - 36,4.104

CuAl2O4 -nt- - 4,58 Khng tng hp -

MnAl2O4 -nt- - 4,12 - - -

FeCr2O4 -nt- >7 4,392 1780 0,90 -


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MgCr2O4 -nt- (8,31) 6 4,429 2330 0,96 10,3.102

ZnCr2O4 -nt- (8,31) >7 5,393 - + 97,2.102

FeCr2O4 -nt- (8,34) - 4,998 2180 0,85 54,7.10

CoCr2O4 -nt- (8,31) - 5,580 - - 40,1.10

NiCr2O4 -nt- - 5,160 - - -

MnCr2O4 -nt- >7 4,870 - - -

CuFe2O4 -nt- - 5,700 - - -

MgFe2O4 -nt- (8,36) 6,65 4,560 1750 1,15 25,1

ZnFe2O4 -nt- (8,42) 6,5 5,330 - - 78,0

CdFe2O4 -nt- - 5,800 - - -

MnFe2O4 -nt- 6 4,900 - - -

FeFe2O4 -nt- (8,40) 6 5,210 1598 1,53 5,4(300o)

NiFe2O4 -nt- (8,35) 5 5,340 51,3

CoCo2O4 -nt- - 6,073 P.hu - -

MgCo2O4 -nt- - 4,960 - - -

MgV2O4 -nt- (8,42) - 4,240 - - -

CaV2O4 -nt- - 4,570 - - -

MnV2O4 -nt- (8,52) - - - - -

BeAl2O4 Hnh thoi - 8,5 3,720 1870

ph

0,573

BaAl2O4 Lp

phng

8 - 1820

Mg2TiO4 Lpphng

>6 3,560 1,12

Zn2TiO4 Lp

phng

5,360

Mn2SnO4 Lp

phng

4,640 1850 - -

Vai tr ca sxen phobitan d cng nh hng mnh n tnh dn in. V dspinenLiMn2O4v LiV2O4u c cu trc ging nhau l Li[Mn

3+Mn4+]O4, Li[V3+V4+]O4.

Trong chai spinen, vtr bt din u cha ng thi mt loi cation c mc oxi

ho khc nhau l +3 v +4. Tuy nhin, sxen phd trong vanai ln hn trong mangan, iuny c phn nh tnh cht in, LiMn2O4l cht bn dn theo cchnhy, cn LiV2O4l cht dn in kiu kim loi.

Vn nghin cu tng hp spinen v nghin cu tnh cht quang, cnhit, in, tcachng l i tng ca nhiu nh ho hc v c. Theo dn in c thnh gi gin tipvcu to bn trong ca spinen cng nhca dung dch rn spinen. Vdn in th c thxp cc spinen thuc vloi hp cht bn dn v c thphn thnh 3 nhm:

Aluminat c dn in rt b (in tr ring 990oC R = 105106 m.cm),cromit c dn in trung bnh (R 990oC t103104 m.cm), ferit c dnin cao (R 990oC t10102 m.cm) ring FeFe2O4 c dn in gn bng dn in ca kim loi.


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Trong aluminat, tnh dn in c quyt nh bi cation ho tr2, cn cromit v ferit (trhp cht FeO) li c quyt nh bi cation ho tr3.

Mt trong cc c tnh quan trng ca spinen l ddng to thnh dung dch rn thay thvi nhau do thng smng ca chng gn bng nhau.

V d, cc hspinen MgAl2O4-MgCr2O4, FeCr2O4-FeFe2O4c gin trng thi thuckiu tnh tan khng hn ch. Cromit cng dtrn ln vi ferit. Mt sspinen c thto dungdch rn vi nhm oxit, c bit vi -Al2O3c mng li ging vi mng li tinh thcaspinen. Ni chung, tnh cht ca spinen c quyt nh bi tnh cht v hm lng ca ccoxit hp phn. Khi tng hp spinen hoc khi hnh thnh dung dch kiu spinen u c stngthtch ca pha tinh th. Mt nt c trng cn quan tm l phn ng thay thtrong spinen, vdcc aluminat vi oxit c 3 kiu tng tc:

1) MgO + BeAl2O4 = MgAl2O4+ BeO

2) MgO + NiAl2O4= (Ni,Mg)O + (Mg,Ni)Al2O4

3) Cc aluminat trn ln hon ton cn cc oxit th trn ln khng hon ton. V dtrongcc hoxit km.

c tnh rt quan trng i vi k thut ca spinen l chu la cao, bn vi cc tcnhn oxi ho cng nhtc nhn kh(xem bng 10).

Trong cc spinen trn y th FeFe2O4c ngha quan trng nht, trong st hai mcoxi ho l II v III. Da vo kt qunghin cu dn in v ttnh c thkt lun c rngFeFe2O4 thuc kiu spinen nghch o, ngha l Fe

IInm trong hc O cn FeIIImt na nmtrong hc O, mt na nm trong hc T.

Vi cc ferit c thbiu din bng cng thc tng qut sau:

_ _

2 3 2 3x 1 x 41 x 1 x

M Fe [M Fe ]O+ + + ++

Trong cation nm trong hc T c t ngoi du mc, cn nm trong hc O th trong du mc.

Khi x = 1 ta c spinen thun, x = 0 ta c spinen nghch o. Spinen trung gian th 0 < x Rc/Ra> 0,732 8 Kiu CsCl

0,732 > Rc/Ra> 0,414 6 Kiu NaCl

0,414 > Rc/Ra> 0,225 4 Kiu blend ZnS, vuazit ZnS

Cn lu rng khnng sdng quy tc tlbn knh ca ion on bit SPT v kiucu trc rt hn ch. Thc ra quy tc ny ch c ch gii thch khuynh hng chung mthi. Gi trtuyt i ca tlbn knh Rc/Raphthuc vo hn vbn knh ta sdng.

Nu sdng hn vbn knh ion ca Paoling v Golsmit (ngha l RO2=1,40) th RRb+/RI= 0,69, do SPT ca Rb+bng 6 v RbI c cu trc kiu NaCl. Nu sdng hn vbn

knh ca Shannon (ngha l RO2=1,26) th RRb+/RI= 0,8, do SPT Rb+bng 8 v RbI c

cu trc kiu CsCl. Vi LiI cng c hai gi trtlRc/Ral 0,28 v 0,46. Nu nhn l 0,28 th

SPT ca Li+

l 4. Nhng thc tSPT ca Li+

bng 6 ngha l tl phi bng 0,46.


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Bng 23TlRc/Ra, SPT ca cation v kiu cu trc ca oxit ccng thc MO2Oxit Rc/Ra SPT Kiu cu trc xcnhc

SiO2 0,32 4 Silic oxit (SPT 4)GeO2 0,430,54

46

Silic oxit (SPT 4)Rutin (SPT 6)

TiO2 0,59 6 Rutin (SPT 6)SnO2 0,66 6 Rutin (SPT 6)PbO2 0,73 6 Rutin (SPT 6)HfO2 0,67

0,7768

Rutin (SPT 6)Florit (SPT 8)

ThO2 0,95 8 Florit (SPT 8)

Vi hp cht ca oxit hoc florua c cng thc AB2th c ba kiu cu trc l silic oxit(SPT 4), rutin (SPT 6) v florit (SPT 8) (xem bng 23).

Khi gi trRc/Rang vi khong bin gii chuyn kiu cu trc (0,732 hoc 0,414) th

hp cht c thtn ti di hai dng th hnh. V dvi GeO2, HfO2,Khi kho st mng li tinh thion ngi ta thng sdng khi nimphn in tch

ca ionhoc lc ho trca lin kt. V dcation Mm+c bao quanh bng n anion Xnthlc ho trca lin kt gia cation Mm+v mt anion Xnl = m/n. in tch m ca mtanion phi bng tng lc ho trca cc cation bao quanh anion , ngha l = m/n. V dspinen MgAl2O4gm c phn mng anion O

2xp kht kiu lp phng mt tm ABCABCA,ion Mg2+ nm cc hc t din (SPT 4), ion Al3+ nm cc hc bt din (SPT 6), xungquanh ion O2c 3 cation Al3+v mt cation Mg2+:

i vi Mg2+: phn in tch dng cho 1 ion O2= 2/4 = 1/2

Vi Al3+: phn in tch dng cho 1 ion O2= 3/6 = 1/2Vy phn in tch dng ca 1 ion O2trong MgAl2O4l:

3Al3++ 1Mg2+= 31/2 + 1/2 = 2

C thchng minh rng trong cu trc silicat khng thc 3 tdin SiO4ni chung vinhau qua nh. V rng phn in tch dng cho mt ion O2trong tdin SiO4l 4/4 = 1,ngha l O2chchung cho 2 ion Si4+v sc phn in tch dng tng cng l 2. Nu 3 tdin SiO4ni chung vi nhau mt nh oxi th phn in tch dng tng cng ca oxi bng3, l iu khng cho php.

Bng 24 gii thiu lc ho trca lin kt ca mt scation. Da cc sliu trong bng24 chng ta c thhiu c cch thp cho php v cch thp khng cho php khi ghpcc a din trong mng li tinh thoxit.

Bng 24Lc ho trca lin kt ca mt scation

Cation SPTLc ho trca

lin ktCation SPT

Lc ho trca lin kt

Li+ 4; 6 1/4; 1/6 Al3+ 4; 6 3/4; 1/2Na+ 6; 8 1/6; 1/8 Cr3+ 6 1/2Be2+ 3; 4 2/3; 1/2 Si4+ 4 1Mg2+ 4; 6 1/2; 1/3 Ge4+ 4; 6 1; 2/3Ca2+ 8 1/4 Ti4+ 6 2/3Zn2+ 4 1/2 Th4+ 8 1/2


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Cho n by gichng ta vn githit rng trong mng tinh thion chc thun tu llin kt ion, bn cht lc lin kt trong mng li chthun tu l lc ht tnh in gia ccion tch in ngc du. iu ny khng ng vi thc t, v dtrong mng tinh thca KCl,in tch xc nh c ca cc ion khng phi bng 1 m l 0,76. iu ny c ngha l

gia ion kali v ion clo c 24% l lin kt cng ho tr, lin kt ion chchim 76%.Bng 25Cch ni cho php v cch ni khng c php ca cc a din oxi qua nh chung

Cho php V dpha rn Khng c php

2SiO4(T) oxit silic >2SiO4(T)1MgO4(T) + 3AlO6(O) spinen 3AlO4(T)1 SiO4(T) + 3 MgO6(O) olivin 1 SiO4(T) +3AlO4(T)

xc nh mc lin kt cng ho trtrong mng li tinh thion, Sanderson ara mt phng php mi. Phng php ny da trn csthang in m ca cc nguyntdo ng xy dng. Theo ng th m in l o sc ht gia in tch dng hiu dngca ht nhn nguyn t ca nguyn t vi in t ngoi cng, ngha l m in linquan n mc chc c ca nguyn t. nh gi m in S ng sdng cng thc:

aD

D=S (14)

trong D: mt in ttrong nguyn tc xc nh bng tlgia nguyn tsvthtch nguyn t, Da: l mt in tkhi ngoi suy tuyn tnh tgi trD ca nguyn tkhi trthnh kh tr. Bng 26 gii thiu thang in m ca Sanderson.

Khi cc nguyn tc m in khc nhau lin kt vi nhau to thnh hp cht hohc th c ssan bng m in cc nguyn t trong hp cht u c gi trm

in trung bnh ( S ) bng nhau.V dvi NaF c Na FS S .S 2,006= =

vi BaI2c 23 Ba IS S .S 2,26= = .

Scn bng m in c ngha l trong lin kt gia cc nguyn tkhc nhau th ccin tlin kt blch vpha nguyn tc m in ln hn, lm cho nguyn t din tch m, cn nguyn tc m in b hn th din tch dng. Phn in tch d

() bng tlbin thin m in ca nguyn t (S) vi gi tr( cS ) khi githitin tlin kt i hn vpha nguyn tc m in cao to thnh ion c mt n v

din tch 1.

c

S

S

=

(15)

trong :

S = S S , cn S08,2=S C (16)


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Bng 26m in v kch thc nguyn tca mt snguyn t

Nguyn t SBn knh cng ho tr

Rc()B (i vi trng thi

rn) SC ri()H 3,55 0,32 3,92Li 0,74 1,34 0,812 1,77 0,53Be 1,99 0,91 0,330 2,93 0,58B 2,93 0,82 2,56C 3,79 0,77 4,05N 4,49 0,74 4,41O 5,21 0,70 4,401 4,75 1,10F 5,75 0,68 0,925 4,99 1,61Na 0,70 1,54 0,763 1,74 0,78Mg 1,56 1,38 0,349 2,60 1,03Al 2,22 1,26 3,10Si 2,84 1,17 3,51P 3,43 1,10 3,85

S 4,12 1,04 0,657 4,22 1,70Cl 4,93 0,99 1,191 4,62 2,18K 0,42 1,96 0,956 1,35 1,00Ca 1,22 1,74 0,550 2,30 1,19Zn 2,98 3,58Ga 3,28 3,77Ge 3,59 1,22 3,94As 3,90 1,19 4,11Se 4,21 1,16 0,665 4,27 1,83Br 4,53 1,14 1,242 4,43 2,38Rb 0,36 2,16 1,039 1,25 1,12Sr 1,06 1,91 0,429 2,14 1,18Ag 2,59 1,50 0,208 1,29Cd 2,84 1,46 0,132 3,35 1,33

Sn 3,09 1,40 3,16-3,66Sb 3,34 1,38 3,80Te 3,59 1,35 0,693 3,94 2,04I 3,84 1,33 1,384 4,08 2,71Cs 0,28 2,35 0,963 1,10 1,39Ba 0,78 1,98 0,348 1,93 1,63Hg 2,93 3,59Tl 3,02 1,48 2,85Pb 3,08 1,47 3,21-3,69Bi 3,16 1,46 3,74

Khi xc nh c ta tnh c phn lin kt cng ho trtrong hp cht, ng thi tnhc bn knh nguyn tca cc nguyn ttham gia lin kt.

Paoling v Sanderson a ra cng thc kinh nghim xc nh bn knh nguyn tnhsau:

r = rcB (17)

trong : rcl bn knh cng ho tr, l phn in tch dca n

B l hng sca nguyn t cho trong bng 26

Xt vi v d:

Xc nh phn lin kt cng ho trtrong BaI2v di ca lin kt BaI.

in m trung bnh ca Ba v I trong BaI2.


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23S 0,78.3,84 2,26= =

vy SBa= 2,26 0,78 =1,48

SI= 3,84 2,26 =1,58

Scca Ba = 1,93; ca I = 4,08

Do

Ba= 1,48/1,93 = 0,78; I= 1,58/4,08 = 0,39

Vy trong lin kt BaI c 39% l lin kt ion v 61% l lin kt cng ho tr.

Bn knh nguyn tbari rBa= 1,98 0,348 0,78 = 1,71

Bn knh nguyn tit rI= 1,33 + 1,384 0,39 = 1,87

Khong cch hai nguyn ttrong hp cht (dng tinh th) bng 1,71 + 1,87 = 3,58, thc

nghim xc nh c l 3,59.Bng 27in tch phn v bn knh ca clo trong mt stinh thcloruaHp cht Cl rCl() Hp

chtCl rCl()

CdCl2 0,21 1,24 BeCl2 0,28 1,26CuCl 0,29 1,34 AgCl 0,30 1,35MgCl2 0,34 1,39 CaCl2 0,40 1,47SrCl2 0,43 1,50 BaCl2 0,49 1,57LiCl 0,65 1,76 NaCl 0,67 1,79KCl 0,76 1,90 RbCl 0,78 1,92CsCl 0,81 1,95

Bng 28in tch phn oxi trong mt stinh thoxit

Hp cht O Hp cht -O Hp cht O Hp cht O

Cu2O 0,41 HgO 0,27 Ga2O3 0,19 CO2 0,11Ag2O 0,41 ZnO 0,29 Tl2O3 0,21 GeO2 0,13Li2O 0,80 CdO 0,32 In2O3 0,23 SnO2 0,17Na2O 0,81 CuO 0,32 B2O3 0,24 PbO2 0,18K2O 0,89 BeO 0,36 Al2O3 0,31 SiO2 0,23Rb2O 0,92 PbO 0,36 Fe2O3 0,33 MnO2 0,29Cs2O 0,94 SnO 0,37 Cr2O3 0,37 TiO2 0,39

FeO 0,40 Sc2O3 0,47 ZrO2 0,44

CoO 0,40 Y2O3 0,52 HfO2 0,45NiO 0,40 La2O3 0,56MnO 0,41MgO 0,50CaO 0,56SrO 0,60BaO 0,68

Sdng phng php Sanderson xc nh c in tch phn () v bn knh nguynt ca nhiu hp cht. Bng 27 gii thiu in tch phn v bn knh nguyn t ca clotrong cc clorua kim loi ho tr1 v kim loi ho tr2. Bng 28 gii thiu in tch phn caoxi trong cc tinh thoxit.


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T cc s liu trong bng 27 cho thy in tch ca ion clo thay i t 0,21 (trongCdCl2) n 0,81 (trong CsCl), cn bn knh nguyn tclo thay i t1,24 n 1,95. Sosnh cc gi tr vi bn knh cng ho trca clo l 0,99 v bn knh ca ion clo l 2,18ta thy sai lch qu ln. Tt ccc hp cht trong bng 27 chng ta vn xem nhc mng

li ion v quy cho ion clo c in tch khng i l 1, qul khng ng thc t.Cc sliu trong bng 28 cho thy in tch phn ca ion oxi chthay i trong khong

t0 n 1. Cc tnh ton cho thy ttrc ti nay ta vn xem trong cc oxit c cha ion oxil 2, thm thc tin tch ca ion oxi khng vt qu 1 v trong hu ht trng hp cnnhhn 1.

Cu hi v bi tp

1. Mt mt phng chn 3 trc ca tinh thti cc im ng vi thng sn vl3/2.1.1. Hy cho bit chsMiller (h, k, l) ca n.

2. Chng minh rng trong tbo lp phng th:

a. Mt [111] vung gc vi ng (111);

b. Mt [100] vung gc vi ng (100).

3. Xc nh kiu cu trc ca cc tbo mng li c toca cc nguyn tnhsau:

a. MX: M 1/2 0 0 , 0 1/2 0 , 0 0 1/2, 1/2 1/2 1/2

X 0 0 0 , 1/2 1/2 0 , 1/2 0 1/2, 0 1/2 1/2

b. MX: M 0 0 0 , 1/2 1/2 0 , 1/2 0 1/2, 0 1/2 1/2

X 1/4 1/4 1/4 , 3/4 1/4 3/4 , 3/4 3/4 1/4, 1/4 3/4 3/4c. MX: M 0 0 0

X 1/2 1/2 1/2

4. Xc nh chc c, s hc trng bt din, s hc trng t din ca t bomng li lp phng khi tm, lp phng mt tm, gi ghm chc c lc

phng.

5. Na2O c cu trc kiu antiflorit vi hng smng a = 5,55, xc nh dilin kt NaO, khong cch OO, NaNa, khi lng ring (g/cm3). Cng cuhi i vi CeO2 c cu trc florit a = 5,41.

6. M tcu trc peropkit ABO3. SrTiO3 c cu trc perpkit vi hng smng a= 3,905. Tnh di lin kt SrO, TiO. Xc nh sphi tr ca oxi trongSrTiO3.

7. Xc nh sphi tr ca oxi trong spinen MgAl2O4. Cho bit thng smng can bng 8,09, xc nh t trng (g/cm3). Xc nh thng s oxi ca spinenMgAl2O4, cho bit bn knh ca ion Mg2+ bng 0,74, bn knh ca O2bng1,36.

8. Gisphn mng ion O2trong spinen AB2O4 gi ghm chc c lp phngmt tm l tng. T tnh ton spinen ca cc kim loi ho tr2 v kim loiho tr3 no c thng soxi l tng (W = 0,375).


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9. 9. Ti sao ZnS c tlRc/Ra = 0,63 nhng tbo mng li li khng theo kiuNaCl m theo kiu blend.

chuong 3 cau truc tinh the

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