3r

Abstract Submilted Sorting Category P;\CS Number 74.70Vy ror the March 1990 iVleeUng o r llie Suggested Sess ion :

American I'hysic;lI Society 1Jigh-Tc Superconductors 12-1() ["larch 1990

Electronic Properties of "n_type"' Iligh Temper­ature Superconductors as a Function of Synthesis and Process­ing. P .M. GRANT, M.E. LCWEZ-MORALES* and R..J. SAYOY, IllM Almaden Research Center.-- We report studies on the resistivity, a.c. susceptihility and thermopower or ceramic Nd 2 - xCexCu04_y and Ndl:u04 -Y - Xr X as a runction of prepa­ration and processing. We find that the temperature dependence of p in the normal state, the low-temperature shielding fraction given by Xac, and the sign and magnitude of the thermopower depend strongly on synthetic conditions . Usual calcination methods involving direct reaction or oxides of the constituent cations in a single step result in samples \vitl! non-metallic normal state resistivity, low hulk superconducting fraction , and a Seebeck coefficient which can change sign as a function of temperature. Using a two-step calcination rollowed hy a long anneal time and rapid quenching, material i .~ obtained with bulk superconducting fraction, metallic resistivity and negative thermopower. *On leave from Instituto de Investigaciones en Materiales, UNAM

Signrlture or ;\ PS Member

Paul M . Grant

Nilme of /\ PS Member

I BM Almaden Research Center

Prefer Standard Session Address

San .Jose, CJ\ 95120-6099

ulletin of the American

Physical ociety

Program of the 1990 March Meeting begins on page 160

>

Volume 35, Number 3 March 1990

16:06

K149 Elec tronic I' ropi:rties or "u-typc" Il igh Tem12£!: at urc Superconductor~ as a Fl!llction or Synthesis and Process­~ P.M. (;RANT, . ME. L()I'I~Z-M ()RAI.I;S· and IU . SA VOy. IIlM. Almaden Research Center..:: We report studies on the resistivity. a.c . . ~usceptihility and thermopower or ceramic Nd1_.Ce.CuO• .. y and Nd1CuO. y .1'. as ,I rlllH:tion or prera. ralion and processlllg. We find that the temperature dependence of I' In the normal state. the low· temperature .~hiclding fraction given by be. and the sign <lnd magnitudc or the thermopower depend strongly on synthetic condition .~. {Isual calcination methods involving direct react ion or oxides or the constituent cations in a single step re.qlit in s~nlples with non-metallic normal state resistivity. low hulk superconducting rraction. and a Seeheck 'eoefficient which can change sign ;r .~ a rllnction or temperature. \Jsing a two-step calcination followed hy a long an neal tllne and rapid quenching. material i~ ohtained with hulk superconducting rraction, metallic I'c .~is tivity and negative thermopower. 'On leave rrom IMtituto de Investigaciones cn Materiales. UNAM

10:18

!-:' 141O Neutron Irradiatjon Effects of Un-dooed and Doped Tl-8a-Ca-Cy-O Supercoducting Samples. J.M.M~ason and Z.Z.Sheng, Department Qf ~, ~.~lrlc~, Department of Chemical Engineering, ~nlverslty of Arkansas. -- Various un-doped and Ag- or Hg-doped Tl-8a-Ca-Cu-O samples were exposed to dlfferent lev~ls o~ neutron radiation and were compared to thelr non-lrradlated counterparts by resistance m~asurem~nt, ac susceptibility measurements, and x-raydlffractlon analysis_ Interesting differences between the irradiated and non-irradiated samples were observed.

16:30 K14 II Impurity Effect .of S on SuperconductIvity In

YBa2CU3S06-<>· J . T. Wang. Stanely Tsai. Willie Williams, and

Saligrama SubbaRao Lincoln UnIversity, Lincoln UniversIty,

PA 19352 A. Kebede and J . E. Crow Temple UniversIty,

PhiladelphIa, PA 19122 -- We have studied the temperature

dependence of resistivity. magnetization of YBa~Cu .1so 6-<> to

determine the effect of the substitution of 0 by S . It has been

found that the transition temeprature Tc Is about the same as

YBa lCU307..,f, . It shows no isotopic effects; however, the

susceptibility of YBalCulSO~6 has remarkable difference from

that of YBa2CU307..,f,. The curve of susceptibility YBa2CUlS06-<>

above Tc can well be fit by the Curie-like law.

'This work is supported by ONR Grant NO. NOO014-89-J-3237.

16:42 K1412 Superconductivity in the Pre sence of Strong Parama netism: ( 7Ca )Sr (TI Pb )Cu 0 (R =

Magnetic Rare Earth Element. K_ Chen, Y.T. Huang, S.W. Lu, and W.H. Lee, Materials Research Laboratori ­es, Industrial Technology Research Institute, Chutung, Hsinchu, Taiwan R_O.C .. *-- The electrical and magnet­ic properties of the monophasic polycrystalline supe­rconductors (Ro.2Cao_s)Sr2(Tlo.SPbO.S)CU20y (R = mag­net lc tare earth element), which crystalize in the YBa2Cu307_x-like tetragonal structure with space gro­up P4/mmm, have been investigated. One interesting phenomenoo is the observation of the s trong paramagn­etism induced by the low-field-cooled trapped flux. For the compounds with effective moment larger than ­7 ~B' the magnetic susceptibility became positive be­low Tc wh en the applied magnetic field was 'i ncreased to - 2 Tesla. DC electrical resistivity meas urements under these magneti c fields reveal the fact of incom-

Vol. 35, No.3 (I 990)

Wednesday Afternoon

pletely burried diamagne ic l 'gnal by the magnetic !ield induced paramagnet i m.

Supported by the Ministl ot conomic Affairs, Rep­ublic of Chioa, no. 33Bl000 to ITRI.

SESSION K1S: HIGH T< THEORY: ANYONS Wednesday afternoon, 14 March 1990 San Simeon A Room at 14:30 D. Lee, presiding

14:30 K151. Anyon Superconductivity. Y-H Chen, F. Wilczek, E. Witten, B. Halperin, Institute for Advanced Studies' - We in.vestigate the statistical mechanics of a system of p~icles W1th fractional statistics (a.nyons) in 2+1 dimensions. We study the mean field theory of anyons. Based on the RPA, we study the superfluidity (or, superconductivity after coupling to elec­tromagnetism) of Anyon gas for statistical parameter 9 = '/l"(1- . l i n). Large n approximation is taken to study the low energy excitations. We study the phenomenology of anyon supercon­ductivity by mapping the response function from RPA to that of an effective lagrangian.

1 Y.-H. Chen, F. Wilczek, E . Witten, B. Halperin, Int. J. Mod. Phys . B S, 1001(1989).

14:42 K15 2Collective Behavior of Anyons. C.B. HANNA. A.L. FE11 and R.B . LAUGHLIN. StanFord University -- The undamped linearly-dlsperslng collecttve mode and the Meissner effec of the fractional-statistics gas are explained in terms of simple generalization of Llndhard screening . The collective-mode spectrum is obtained both variationally an in the random-phase ' approximation.

14:54 K 15 3 Band Structure of the Flux Lattice. D .P. AROVAS· and F.D.M. HALDANEt, Unjversity of California. San Djel:o -- As an approximation to the many anyon problem, we have investigated the band structure of a charged particle in the presence of a two-dimensional lattice of flux tubes. Various features of the dispersion are sensitive to the arithmetic ratio p/q, where <I>=p/q'hc/e is the flux per tube. For p­=1, q>2, there appear to be (q-2) extremely flat low-lying magnetic Bloch bands, reminiscent of a Landau level structure. Degeneracies and "flux smearing" are also discussed.

* NSF Presidential Young Investigator and Alfred P. Sloan Fellow. ** Supported in part by NSF: DMR-8901985.

15:06 K 15 4 Noncommutatjye Geometry Instead of Nal:aoka's Ground State and Pennj-LiQuid Breakdown in Correlated Electron Systems. P. WIEGMANN, University of California San Diel:o -- t'-rguments suggesting that in two dimensions the ground state of correlated electronic systems violates parity and time reversal are presented. It is shown that quasi-particles acquire fractional statistics and fonn an anyon gas.

15 :18 K 15 5 SuperfJlljdjty ofthe Lattice Anyon Gas and Topological lnyarjance. Eduardo Fradkin", Department of Physics, Uoiversity of Illinois at Urbana·Champaign, 1110 W.Green St., Urbana IL 61801. I consider a gas of"free" anyons with statistical pare meter 0, with hard cores, on a two dimensional square lattice. I map this problem onto a gas of fepnions coupled to a Chern-Simons gauge theory with coupung e=-. At the semi­classical level, the system is fOWld to be equivale~ to a gas of fermions , with the same density, in an average efective magnetic field ~. I consider the case in which an integer number of the Landau baods of the sapdle point problem are completely filled. If o~ and the density p=-, with m, r and q integers, the system is a s~perfluid, provided th?!t q is larger than twice the largest com mon factor of m and r . If q is even and the system is half

583

Electronic Properties of "n -type" High Temperature Superconductors

as a Function of Synthesis and Processing

P. M. Grant . M. E. Lopez-Morales·

R. J. Savoy

IBM Almaden Research Center

• On leave from IIM-UNAM, Mexico City

Appearing in Journal of Materials Research

- -- - - ---------

"n-type" High-Tc

~

Nd a:+-; @ (Ce) v~Clf?)

CUO~

• Nd2Cu04 Host

o Long History (> La2Cu04) o Cu-Q Planes: No Apical Q

• 1988 SC Discovered (Tokura, et al.)

o Doped with 4+ Cations o Negative Hall and TEP at 300K

One-Step Synthesis

(1-0.5x)Nd203 + CuO + xCe02 -7

Nd2-xCexCu04 + O.25x02t

• Synthesis/Processing

o Calcine at 950°C o Sinter at 1050-1150 °C o Reduce under Argon o Rapidly Quench

• Difficulties

o Strong Ce-O Bond o Slow Ce Diffusion o High Temperatures Needed o No Oxygen Reduction Control

,..-..... (f)

+-' C

:::> OJ >

+-' o OJ

0::::

I

~

@~ Nd~ © (Ce) •~CJl?)

cu~

I

1

I I

Nd1.8SCeO.1SCU04-y

I NdCe03.5

~ NdCeJ07.5

- - ~ CU20

I

lI I

Vj J ! UlA-VVv-.A A j

I I I~IIN

I N

0 0~ ~ o to ~

r-­N ~ 'I' N N~0 ~ 0 a0 ~ 0 ~0a to

-~ 0 -­0 -('oj ns: 0

~ N

n S

I I I I ' .

10 20 30 40 50 60 Diffraction Angle (20)

----0

§ Q

[}

0.01 0

8

0.00 0

0.04

0.03

~

E

a0 0.02

'--""

Q..

0.01

0.00 0

0.04

0.03 E

e0

0.02 0 '--""

10 20 30 40 50 Temperature (K)

0

8 8 § 0

0

0

0 Nd 1.85CeO.15CU04-y

~ 0

50 . 100 150 200 250 . 300 Temperature (K)

,--.... (f)

-+-' C

:::l

Q)

.> -+-' 0 Q)

~-0 0

><

i ~

0 0

~

Q)

> --+--J o Q)

~

(,) o

><

~ o 10 20 30 40 50, Temperature (K)

0 50 100 150 200 250 ' 300 Temperature (K)

Two-step Synthesis

I. O.5Nd203 + Ce02 4 NdCe03.5

• Calcine at 1400 DC, 48 hrs, in air

II. (1-x)Nd203 + xNdCe03.5 + CuO 4

Nd2-xCexCu04 + O.25x02t

• Calcine at 980 DC, 24 hrs, in 02 • Sinter at 1050 DC, 48 hrs, in O2

. • Anneal at 980°C, 36 hrs, in Argon • Quench to 25 DC, 30 sec, in Argon

NdCe20 / x

(a)

5011

.. ' ,- . _.

" r tI

/ t:::

r ." " .41' _.,,­I :

-1# '- ~"

"

.~. ' • ..... - . .-' ~

I •

(b)

--

--

8

6

E

a u

4 E Q

2

0

0

0

0

0

0

0

0

0

0

8 0

(c) Nd1.85CeO.15CU04-y

Ar Annealed, 36 Hrs Quenched

8 f-

I

6

-­E 0 a 4 E-­Q

2

f-

f­

-

o -I

0 10 20 30 40 50 Temperature (K)

I I T -

f? CO coo 0 cxx:o 000_

0

0

0

0 -

0

0

0 -

0

~ cf)0~ -

I I I

o 50 100 150 200 250 300 Temperature (K)

0.0

-0.2

S' -0.4 E Q) ~

u 0

>< I;:: ~ -0.6

-0.8

-1.0

I I I I

I- cUDodb~o 0

0

0 00000 ­o 0

0

L­ 0 -

0

L­

0 0

0 -

- # ,0

I 0

-

I--

Nd 1.85CeO.15CU04-y

Ar Annealed, 24 Hrs Quenched

-

- -

I I I I

10 20 30 40 50

Temperature (K) 0

--

1

0.0 T I 1

\ -0.2 I- a ­a

a----. a~ ~ a ~ -0.4 - a ­0 a

a

-0.6 a ­

U1

I- a a

a I I I I-0.8 ----.

~ 0 10 20 30 40 50 ~ ~ -1 Temperature (K) '--'"

(/)

T a

-2 1

-3 ~--~----~----~--~~~~----~ o 50 100 150 200 250 ' 300

Temperature (K)

Summary

o Successes

o Two-Step Method -t Uniform Cex

o dp/dT > 0, T > Tc o Narrow Transition Width o High Diagmagnetic Fraction

o Negative TEP, Tc< T < 300 K

• Unresolved Issues

o Oxygen Distribution o Microstructure

o o

o 0 o

~

0 0 o

s 0

cO 0 s ~o

(DO o o

oo