preparation of new ternary nitrides camn (m=co, ni)

Solid States lonics 63-65 ( 1993 ) 148-153 North-Holland

SOLID STATE IOIIICS

Preparation of new ternary nitrides CaMN (M = Co, Ni )

T. Y a m a m o t o , S. K i k k a w a a n d F. K a n a m a r u The Institute of Scientific and Industrial Research, Osaka University, Osaka 567, Japan

Reactions between alkaline earth nitrides and transition metals were investigated in relation to CaNiN, which contains infinite linear Ni-N chains separated by square arrays of Ca ~+. Ca~ _~SrxNiN solid solutions with CaNiN type structure were obtained in a region ofx < 0.75, but the product with x= 1.0, SrNiN, may be isostructural with BaNiN having zigzag Ni-N chains. The Ca (Ni, Co)N solid solution was not formed and a compound with a possible composition of Ca3CoN3 was obtained in the reaction between Ca3N2 and Co in N2 gas. The X-ray diffraction pattern was fully indexed with an orthorombic crystal lattice with a = 5.84 A, b=4.79 A, c= 12.06 A. The Ca~ _xSrxNiN solid solutions were metallic conductors and Ca3CoN3 was a semiconductor with E. = 0.03 eV. Structural relations to other kinds of alkaline earth-transition metal nitrides are discussed.

1. Introduction

Metal ni tr ides exhibit a variety of chemical bond nature and are at t ract ive in a wide field of mater ia ls science such as ion conductors, high tempera ture structural materials, superconductors and so on. Most of ni tr ides s tudied so far were s imple metal ni t r ides such as TiN, AIN and Si3N4. We have a great interest in double metal ni tr ides which consist of metal ni- tr ides with different bond nature, and have found new ionic conductors Li3BN2 [ 1 ], LisSiN4 [2 ] etc. We also repor ted superconduct iv i ty in a b inary solid solution prepared under high pressure between metallic N b N and covalent GaN [ 3], and intensively improved oxidat ion-durabil i ty of TiN dissolving AIN [4 ]. Recently the compound CaNiN was discovered by Disalvo et al. [ 5 ], in which one-dimensional N i - N chains were combined in an unusual three-dimensional arrangement . The formal valence of Ni cat ion was + 1. It is a very uncommon valence for Ni in oxide and its electron configuration is d 9, which is the same as that o f Cu 2+ in high- temperature superconductors . However CaNiN remains metall ic and paramagnet ic down to low temperature . There has been no further informat ion on this compound, except electronic-structure calculations [ 6 ]. Several kinds of alkaline ear th- t ransi t ion metal nitrides, e.g. Ca3Vl~3 [7 ], Ca3CrN3 [8 ], Ba3FeN3 [9] , BaNiN [ 10 ], BaaNi6N7 [ 11 ] etc., have been repor ted since

the discovery of CaNiN. We could not f ind any re- ports on the double metal ni t r ide containing cobalt.

In the present investigation, we examined the react ions in both Ca 3N z -S r /N -N i and Ca3N2-Ni -Co systems, in N2 gas. The prepara t ion and propert ies of Cal_~SrxNiN solid solution and Ca3CoN3 will also be reported.

2. Experimental

Calcium ni tr ide ct-Ca3N2 and s t ront ium ni tr ide Sr2N were prepared, respectively, by heating calcium metal (Showa Electric Ind. Ltd., 99.99%) and stron- t ium metal granules (Nacala i Tesque Co. Ltd., 99.9%) in N2 gas (Osaka Oxygen Ind. Ltd., 99.9999%). They were allowed to react for 2-3 h, respectively. In tempera ture ranges of 948-1223 K for Ca3Nz and 643-873 K for Sr2N.

The Ca3N2 and Sr2N thus obta ined were mixed with Ni and Co metal powders (Nakara i Tesque Co. Ltd., 99.9%) in appropr ia te molar ratios. Starting mixtures were then pressed into pellets and heated as 1273 K in N2 gas for 20-36 h. Ca3N2 and Sr2N have been repor ted to sublime slowly at 1273 K [5 ]. They are also very sensitive to small amounts o f 02 and H20 remaining in NE gas, which produce CaO and SrO. Therefore the following special care was taken to prevent these difficulties: ( i ) all such treat-

0167-2738/93/$ 06.00 © 1993 Elsevier Science Publishers B.V. All rights reserved.

T. Yamamoto et al. / New ternary nitrides CaMN 149

ments as mixing, grinding and pressing into pellets were carried out in a helium-filled glove box, because Ca3N2 and Sr2N and their products are air-sensitive; (ii) the pellets were also sandwiched or covered with calcium nitride to prevent the oxidation and evaporation of alkaline earth metals in the pellets.

The products were identified by the powder X-ray diffraction method using a diffractometer with Cu Ka radiation monochromatized with pyrolytic graphite. The samples were loaded onto a silica glass plate. They were set into a holder covered with a 0.007 mm- thick aluminum window to avoid air exposure. The nitrogen content was evaluated by the modified Du- mas method. Electrical resistivity was measured on sintered pellets by the four-probe method in a temperature range from 100 to 300 K. Sample dimen- sions were 5 × 15 X 0.5 mm. Silver electrodes worked in ohmic contact. The sample holder was sealed in an argon-filled silica tube, and the measurements were performed through the lead wire.

3 . 0 -

3.6

c

a

O 0 O

i I i 0.0 0,5 1,0

x i n Cal_xSrxNiN

11.4

7.2 ~" t9

T.O

Fig. 1. Tetragonal lattice constants a and c against the amount of strontium x in the Cat_~SrxNiN solid solution. Open and filled circles represent a- and c-parameters, respectively. Squares are values for the hypothetical compound SrNiN with CaNiN type structure.

3 . R e s u l t s a n d d i s c u s s i o n

3.1. Reactions in the Ca3N2-SreN-Ni system

CaNiN and the Ca~_xSrxNiN solid solution were synthesized from the mixture of Ca3N2, Sr2N and Ni metal at 1273 K in N 2 gas. The products contained a small amount of CaP, SrO and Ni metal as im- purity phases. The X-ray diffraction pattern of the main phase showed that CaNiN type Ca~_~SrxNiN solid solution was obtained in a limited compositional range up to x=0.75. It has a tetragonal crystal lattice and the lattice constant increased with increasing x in this compositional range, as shown in fig. I. The lattice constants at x--0.0, a--3.5807/~, c= 7.0079 (7) A, are the same as the reported values for CaNiN [5], a=3 .5809(2) A, c=7.0096(3) /~. The lattice constant c remarkably increased from 7.0079/~ to 7.3415/i with an increase of strontium context x. However, the lattice constant a depended only slightly on x, increasing from 3.5807/~ to 3.6063 /~. The layers of one dimensional N i -N chains run- ning along ( 1 0 0 ) or (0 I 0 ) in CaNiN stacked in a three-dimensional manner as shown in fig. 2. It is very easy to imagine that the interlayer distance can

a la

Fig. 2. Schematic representation of crystal structure of CaNiN (a) and BaNiN (b). Open large, small and filled circles represent the nitrogen, alkaline earth and nickel atom, respectively.

expand, but the a-axis, corresponding to twice the Ni -N distance in the chain, expands very slightly with the substitution of Ca 2+ by Sr 2+. The bond distance in similar one-dimensional N i -N chain has been reported to be 1.83/~ [ 12] for Ni2N. The observed Ni - N distance in the linear chain ranging from 1.7904 /~ to 1.8032 A is rather shorter than that in Ni2N. The N i -N distance in hypothetical SrNiN with the CaNiN type structure was evaluated to be 1.8055 ~, by extrapolations of the observed values of solid so-

150 T. Yamamoto et al. / New ternary nitrides CaMN

lutions. This value is still smaller than 1.83 A in Ni2N. However SrNiN was not isostructural with CaNiN as will be ment ioned later. Factors other than the N i - N distance may therefore play an impor tan t part in forming the CaNiN type structure. The alkaline earth ions in the CaNiN type solid solut ion are tetrahe- draly coordina ted with four N atoms. The N - N distances in the N4 te t rahedron are shown as a function of Sr content in fig. 3. The N - N dis tance in the layer is shorter than that between the layers, indicat ing the deformat ion of the N4 te t rahedron in such a way that the te t rahedron is elongated along the c-axis. The devia t ion from an ideal te t rahedron increases with increasing Sr content, which may be related to the present observat ion that SrNiN takes a different structure than the CaNiN type structure.

The tempera ture dependence of the electrical resist ivity in a tempera ture range from 100 K to 300 K is shown in fig. 4. CaNiN exhibi ted metall ic con- duct ivi ty as repor ted by Disalvo et al. [5] . Both magni tude and tempera ture dependence of the resist ivity were almost the same as those already reported. All Ca~ _~SrxNiN solid solution samples also showed metall ic behavior . The resistivit ies were of the order of 10 -4 ~ - c m for solid solutions up to x = 0 . 5 . While the value o f resist ivity increased in more than one order of magnitude for x=0 .75 , it still showed metall ic tempera ture dependence. The in-

.,<: 3.6

3.5 0.0

0 d~

o

0

• • dc

i I i

0.5

x i n C a i _ x S r x N i N

4.5

4 . 4

4.3

1.0

- 4

Fig. 3. The N-N distances in the N4 tetraheron in the Cat_~SrxNiN solid solution with CaNiN type structure. Filled and open circles represent the values in the linear chain (de) and the interlayer (dr), respectively.

8 i I I

¢l

& l

4

c~ 2

X

x X~ ×x xxx

xx×X xxx

x xxx

xxX XX X X

X x X x

~¢~<X xxx

. . . . . . . . ~ _ ~ ~ 0 -I- . . . . . . . . r . . . . . . . . -I- , I

100 200 300

T / K

Fig. 4. Temperature dependencies of electrical resistivities of the Ca~_~SrxNiN solid solution with CaNiN type structure. Open and filled circles, ( + ) and ( × ) represent the values for x = 0.0, 0.25, 0.50 and 0.75, respectively.

• ~ b

2 0 4 0 6 0 8 0

20 / * (Cu-gQ)

Fig. 5. Powder X-ray diffraction patterns of CaNiN (a) and SrNiN (b).

terlayer distance and also the C a - N and C a - N i distances remarkably increase with an increase ofx. This fact may mean a lowering of the three-dimensional nature in the CaNiN type structure, causing a sig- nificant decrease in electrical conductivi ty.

The product obtained from the mixture with x = 1.0 at 1273 K was black and stable in air, compared to alkaline earth nitrides. The chemical composi t ion o f the product was es t imated to be SrNiNLo. Fig. 5 shows the powder X-ray diffract ion pat terns of SrNiN. The diffract ion pat tern can be indexed as isostructural to BaNiN with an or thorombic cell as seen in table 1. The lattice parameters are

T. Yamamoto et al. / New ternary nitrides CaMN 151

Table 1 X-ray powder diffraction data for SrNiN ")

h k I d~c 6dob, 1/lo h k I d~a¢ do~ I/Io h k I d~c. do~ I/Io

1.761 2 1 ! 1 4.280 4.279 3 4 4 I 1.760 4 7 1 1.398 1 2 1 3.732 3.732 5 2 7 0 1.742 2 9 0 1.396

1.742 8 2 0 1 3.425 3.424 5 1 7 1 1.741 1 9 1 1.396 2 3 0 3.160 4 5 0 1.721 253 1.384

3.155 37 1.722 7 1 3 1 3.155 252 1.718 403 1.381

2.978 3 1 1 3 1.694 4 8 0 1.336 3 2 0 2.751 2.751 3 3 6 1 1.685 1.686 3 2 8 2 1.334 2 4 0 2.670 0 6 2 1.683 6 0 2 1.309

2.668 63 1 4 1 2.667 1 8 0 1.624 1.623 1 0 0 4 1.305 301 2.618 531 1.598 571 1.269

2.618 100 0 0 2 2.609 4 3 2 1.596 1.598 6 4 7 2 1.268 3 1 I 2.568 2.567 4 1 3 3 1.593 6 6 0 1.247

2.516 3 280 1.551 363 1.244 1.552 6

2 5 0 2.283 1 8 1 1.551 5 2 3 1.234 2.282 16

1 5 1 2.281 233 1.524 490 1.232 0 6 0 2.201 2.201 2 54 1 1.522 1.522 16 292 1.231 4 2 0 2.146 442 1.520 73 1 1.210

2.143 3 222 2.140 143 1.517 533 1.208 061 2.028 2.032 6 600 1.513 1.513 13 234 1.206 4 3 0 2.017 303 1.508

2.016 13 2 3 2 2.012 0 5 3 1.453 440 1.870 470 1.451

1.870 23 1.451 4 2 4 2 1.866 5 5 1 1.438 1 5 2 1.819 1.821 2 4 5 2 1.437 1.440 5 07 1 1.774 1 53 1.435

1.397 4

1.384 1

1.336 4

1.311 7

1.270 4

1.247 2

1.233 3

1.211 3

• ) Orthorombic cell parameters: a=9.078(3)/~, b= 13.207(6) A, c=5.219(7)/k.

a = 9 . 0 7 8 ( 3 ) A, b = 1 3 . 2 0 7 ( 6 ) A and c = 5 . 2 1 9 ( 7 )

A. T h e crystal s t ruc ture o f B a N i N is cha rac te r i zed by

an inf in i te N i - N zigzag cha in [ 10 ] in cont ras t to the

s t raight cha in in C a N i N . The re is a n o t h e r s ignif icant

d i f fe rence in crystal s t ruc ture be tween C a N i N and

B a N i N . As seen in fig. 2, C a N i N con ta ins two k inds

o f the N i - N chains; one runn ing a long ( 1 0 0 ) in one

layer and the o the r a long ( 0 1 0 ) in the ad jacen t up-

pe r and lower layers. Th is charac te r i s t ic ar range-

m e n t o f the N i - N cha ins cer ta in ly restr icts the ex-

pans ion o f the a-axis in the C a N i N type Ca1 _~SrxNiN

solid so lu t ion though the c-axis easi ly expands wi th

increas ing x, as shown in fig. 1. Whi le , in B a N i N , the

zigzag N i - N chain runs parallel each o the r only along

the b-axis and Ba ions are also in N4 t e t r ahedra

f o r m e d by folding the N i - N cha ins as shown in fig.

2b. T h e v o l u m e o f the N4 t e t r ahedra m a y be ad-

jus tab le to large a lkal ine ear th ions by vary ing the in te rcha in dis tance. As m e n t i o n e d above , the devia-

t ion o f the N4 t e t r ahed ron f rom an ideal one in

C a l _ x S r x N i N with x < 0.75 increase wi th an increase

o f x, and the C a N i N type s t ructure m a y b e c o m e un-

stable at a c o m p o s i t i o n near x = 1.0, because Sr ions

are too large to be in the te t rahedral site in the C a N i N

s t ructure wi th the l inear N i - N chains. Fu r the r work

is underway to analyze the crystal s t ructure o f SrNiN.

3.2. React ions in the C a 3 N 2 - N i - C o sys tem

The CaNi l _xCoxN sol id so lu t ion was not ob ta ined

unde r the present reac t ion cond i t ions and the pres-

ence o f u n k n o w n c o m p o u n d s was de tec ted at x = 1.0.

T h e p roduc t s wi thou t Ni showed the s imples t pow-

der X-ray d i f f rac t ion pa t t e rn when the rat io o f C a /

Co is 3. The p o w d e r X-ray d i f f rac t ion pa t te rn can be

t en ta t ive ly indexed with an o r t h o r h o m b i c cell wi th

a = 5 . 4 8 A, b = 4 . 7 9 / k and c = 12.06 ,~, as shown in

table 2. The re are several k inds o f a lkal ine earth-

t r ans i t ion meta l n i t r ides wi th a s imi lar c o m p o s i t i o n

to this compound, e.g. Ca3VN 3 [7] , Ca3CrN3 [8] ,

152 T. Yamamoto et al. / New ternary nitrides CaMN

Table 2 X-ray powder diffraction data for Ca3CoN3 a:,.

h k l d~c dobs 1/Io h k / d~,c dobs llIo

0 0 2 6.033 6.037 6 0 0 6 2.011 2.017 20 1 0 0 5.585 5.683 18 1.951 8 0 1 0 4.768 4.833 12 1 0 6 1.892 1.900 14 0 0 3 4.022 4.026 15 2 2 1 1.793 1.802 14 1 1 1 3.473 3.453 15 3 0 2 1.779 1.782 10 1 1 2 3.108 3.093 16 1 1 6 1.759 1.757 15 0 0 4 3.017 3.025 7 3 1 1 1.716 1.711 5

2.851 8 3 0 4 1.584 1.583 7 2 0 0 2.792 2.789 5 2 2 4 1.554 1.559 6 1 1 3 2.693 2.697 100 2 2 5 1.449 1.447 5 0 1 4 2.549 2.547 54 3 2 2 1.426 1.426 10

2.488 21 0 3 4 1.406 t.405 9 0 0 5 2.413 2.422 11 2 3 0 1.381 1.384 6 0 2 1 3.339 2.348 3 2 3 2 1.346 1.344 4 2 0 4 2.049 2.040 6 4 0 4 1.267 1.261 6

~) Orthorombic unit cell parameters: a = 5.48( I )/k, b=4 .79 (2 ) tk, c= 12.06(3)/~.

Sr3FeN3 and Ba3FeN3 [9]. These compounds, A 3 M N 3 , have characteristic structures which contain planar-trigonal [MN3 ]6- ions. The [MN 3 ]6- anions are isoteric to carbonate ion and isolated from each other with alkaline earth ions. C a 3 C o N 3 may also contain planar trigonal [ C o N 3 ] 6- ions.

The temperature dependence of electrical resistivity in C a 3 C o N 3 is shown in fig. 6 in a temperature range of 100 K to 300 K. The resistivity at room temperature was p = 2.55 × 102 f~.cm. The temperature dependence was semiconductive with an ac- tivation energy of 0.03 eV. C a 3 C r N 3 and C a 3 V N 3 ,

,~ 3 U

& r ~

2

Q . !

0 I 100

I

04P • ° o

o o

Qooo o

°°ee°e °° ooooee OOOooq ~

i I i I 200 300

T/K

F i g . 6 . Temperature dependence of electrical resistivity of CaaCoN3.

which contain isolated [ M N 3 ] 6 - anions, are also in- sulating and paramagnetic [7,8]. The semiconduc- rive property contrasts with the metallic nature of the CaNiN, which has linear Ni -N chains. Magnetic measurements and further structural investigation on Ca3CoN3 will reveal its bond nature and electrical configurations.

In summary, we could obtain the CaNiN type Ca~_xSrxNiN (x<0.75) solid solution with linear Ni -N chains, and new SrNiN compounds with zigzag Ni -N chains and C a 3 C o N 3 with trigonal-planar [ C O N 3 ] 3 - . In these compounds, the M-N bond has a large contribution of covalent nature. Examples of simple transition metal nitrides having covalent bond nature have been very limited. FeN with zinc-blend type structure was recently prepared only applying RF-sputter deposition [ 13 ]. The Ni2N type solid solutions, (Nil _xFex)2N and (Nil _xCux)2N, were also prepared by applying RF-sputtering [ 14,15 ]. How- ever, the chemical composition of both solid solutions were limited to a small range of x < 0.2. We recently found a possibility on the formation of an isostructural compound to CaNiN in the reaction of Ca3N2 with Cu in N2. The formation of a double metal nitride of alkaline earth and transition metal seems to stabilize the covalent bonding between transition metal and nitrogen.

T. Yarnamoto et al. / New ternary nitrides CaMN 153

Acknowledgement

We would like to express our thanks to Mr. Ima- bayashi in Showa Electric Ind. Ltd. for supplying calcium granules with high purity. This research was partly supported by Grant-in-Aid for General Sci- ence Research from the Ministry of Education, Sci- ence and Culture of Japan, grants from Iketani Sci- ence and Technology Foundation and from Tokuyama Science and Technology Foundation, and also a grant from the research program on "Creation of New Functional Materials By Nano Synthetic Method" of ISIR, Osaka University, Japan.

References

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[4] M. Takahashi, S. Inamura, N. Nobugai and F. Kanamura, in: Composites and Corrosion/Coating of Advanced Materials, ed. S. Umekawa et al. (Elsevier, Oxford, 1989) p. 307.

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[12] G.J.W.R. Dorman and M. Sikkens, Thin Solid Films 105 (1983) 251.

[13] M. Takahashi, H. Fuji, H. Nakagawa, S. Nasu and F. Kanamaru, Proc. 6th Intern. Conf. Ferrites, Oct. 5-7, 1992, Tokyo and Kyoto ( 1992 ), p. 508.

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[ 15 ] M. Takahashi, K. Ohta and F. Kanamaru, to be published.

preparation of new ternary nitrides camn (m=co, ni)

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