Glassy behavior of Bi2(MoO4)3 single crystal at low temperature

0038-1098/88 $3 00 + 00 Pergamon Press plc

Sohd State Communlcatmns, Vol 67, No 7, pp 723-724, 1988 Printed m Great Britain

GLASSY BEHAVIOR OF KY

BI2(MoO4) 3

Kang, P H

S I N G L E CRYSTAL A T LOW T E M P E R A T U R E

Her*,MS

JangandHK

Klmt

Department of Physics, Pusan Natmnal Umverslty, Pusan, Korea H L Park Department of Physics, Yonsel University, Seoul, Korea and D Fmotello and M H W Chan Department o f Physics, The Pennsylvania State University, PA 16802, USA

(Received 22 March 1988 by J Kanamort) Glassy behawor o f B12(MoO4)3 single crystal at low temperature was first observed The specific heat data below 1 5 K were fitted to C = efT3 + yT, and the parameters were found to be 0t = 13 85, 7 = 15 57 and0n = 2494K frequencies (36, 50, 90cm -l) Ag Raman nodes m B I 2 ( M o O 4 ) 3 showed softening with increasing temperatures This observation m&cates m&rectly that the low lying Raman modes are temperature sensmve and also correlated to the Einstein frequencies typical to the glassy behavior of materials at low temperature The heat capacity was measured by A C technique at &lutmn refrigerator temperature and the resuits are depicted in Figures 1 and 2 In Fig 1, the obtained data were plotted C vs T whereas in Fig 2, C/Tvs T 2 The obtained data below 1 5 K were ftted to the linear term added to the Debye contribution

T H E B I S M U T H sesqmoxlde (B1203) , oxygen conductmg material, has gamed considerable attention recently [1, 2] The oxygen conductivity of B1203 is larger an order of two than the stabdlzed z~rcoma at elevated temperature [3] The B120 3 possesses many slmdarmes to ZrO2 Namely, pure bismuth sesqmox~de has a defect fluorite phase above 730°C which undergoes a destructive phase transmon to a monochnlc structure at low temperature The purpose of this Commumcatmn is to report the first observation of glassy behawor of molybdlte added single phase bismuth oxide compound, t e , B12(MoO4)3 single crystal at low temperature The B12(MoO4)3 is a single phase materml whlch is formed between molybdlte and bismuth sesqumxlde at 500°C through the conventional sohd state reaction techmque Single crystals of B I 2 ( M o O 4 ) 3 w e r e grown by Czochralskl technique and the details were reported elsewhere [4] The space group of BI2(MoO4) 3 was redetermlned by Park et al [5] and found to be p2~/n w l t h a --- 11 01A, b = 11 43A, c = 7 7 3 A a n d f l =

C

=

0~T 3 q-

yT

(1)

Where the coeffioent ~ is simply related to the Debye temperature 0o and ? is the coeffioent of tunneling

50 /,0

103 3 °

The low temperature glassy behavior of materials usually &splays a non-Debye behavior which exhibits a hnear term m specific heat A linear speofic heat term was found and interpreted as the cation tunnelmg contribution [6] Einstein frequencies correlated w~th Raman frequencies m the 28-82 cm-r range has been reported [7] Kang [8] reported that the low

o, 30

.°

:z 20 _'2

E-

%_I0 j o ~

2'5 t All correspondences should be addressed * Present Address Gold Star, Central Research L a b , Seoul, Korea

" ,, 1

l

I

5

75

1

Fig 1 Temperature dependent speofic heat of (MOO4)3 below 1 5 K 723

25

Temperature (K) BI 2-

724

GLASSY BEHAVIOR OF ~0

I

BI2(MoO4) 3

i

S I N G L E CRYSTAL

Vol 67, N o 7

havlor at low temperature reported by Lawless and Swartz [3] Their parameters are a = 17 1, ), = 21 96 and 0o = 294 4 K Thus the glassy behavior was first observed m B I 2 ( M o O 4 ) 3 single crystal at low temperature The origin of abnormal trend of C/T vs T 2 around 0 13 K can not be explained at this stage, but our conjecture is due to crystal Imperfection

20i C/T= 1385T2.1557 (J

10

I

0

5

I

I

I

I

5

75

I

~ 25

Square of Temperafure[lK)z]

Fig 2 C / T v s T 2 for

B12(MoO4) 3

Acknowledgements - - This work is supported by the Korea Science and Engineering Foundation, and the NSF, U S A through Grant No DMR-8206109 (lowtemperature physics)

below 1 5 K

REFERENCES

term In order to interpret the specific heat of glass, Anderson, Halperm and Verma [9] and Phillips [10] (AHVP) mtroduced quantum mechanical two-level state As a source of the two-level state, AHVP proposed tunneling by a single atom or a group of atoms through the barrier of a double-well potential The Debye temperature (0o) was obtained through thermodynam~cal relation

Cv ~- 234NkB -~o

(T 4. 0o) ,

(2)

1 2 3 4 5 6 7

where k Bis the Boltzmann constant The results of this fitting is shown in Fig 2 and the fitting parameters o b t a m e d a r e e = 13 85,7 = 15 57and0D = 249 4 K These parameters he in the same range to that of B1203 + 25 mole % Y203 ceramics showing glassy be-

8 9 10

M J Verkerk & A J Burggraaf, J Electrochem Soc 128, 75 (1981) T Takahashl & H Iwahara, Mat Res Butt 13, 1477 (1978) W N Lawless & S L Swartz, Phys Rev B28(4), 2125 (1984) J H Lee, M S Jang, J S Che & S D Lee, New Physics (Korean Phys Soc ) 25(1), 35 (1985) Y H Park, B G Ann & M S Jang, New Physws (Korean Phys Soc ) 26(4), 266 (1986) D B Mcwhan, C M Varma, F L S Itsu & J P Remelka, Phys. Rev B15, 553 (1977) A S Barker, J r , J A Dltzenberger & J P Remelka, Phys Rev B14, 4253 (1976) K Y Kang, Ph D thests, unpubhshed, Pusan National Umverszty (1988) P W Anderson, B I Halperin & C M Verma, Phtlos Mag 25, 1 (1972) W A Phllhps, J Low Temp Phys 7, 351 (1972)