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THE ULTRASONIC ATTENUATION IN α-LiIO3
CRYSTAL UNDER AN ELECTROSTATIC FIELD
Wang Ji-Fang, Zhang Liang-Kun, Li Hua-Li, Deng Ting-Zhang
To cite this version:
JOURNAL DE PHYSIQUE
C o l l o q u e CIO, s u p p l é m e n t a u n o 1 2 , Tome 4 6 , décembre 1 9 8 5 p a g e CIO-517
THE ULTRASONIC ATTENUATION IN e-LiI03 CRYSTAL UNDER AN ELECTROSTATIC FIELD
WANG JI-FANG, ZHANG LIANG-KUN, LI HUA-LI AND DENG TING-ZHANG
Institute of Physics, Academia Sinica, Beijing, China
Abstract - The attenuation o f longitudinal wave p r o p a ~ a t i n g along the c-direction of a-Li103 c r y s t a l i s increased with an apulied e l e c t r o s t a t i c f i e l d i n the same direction. The whole nrocess showes a relaxation behaviour. The attenuation of shear wave was found t o be independent of the applied e l e c t r o s t a t i c f i e l d . The above pheno- menon i s explained on the bases of the interaction of longitudinal wave with the transporting ions.
a-Li103 belongs t o the hexagonal system with snace grouu
cg
and i s a polar crys- t a l . ünder the e l e c t r o s t a t i c f i e l d , there e x i s t many i n t e r ~ s t i n g phenornena which have been discovered by neutron d i f f r a c t i o n ( I l , l i g h t d i f f r a c t i o n ('1 and dielec- t r i c measurement (3) and so on. I t w i . l l b e of great i n t e r e s t t o explore what haypens when the e l e c t r o s t a t i c f i e l d a c t s on the c r y s t a l through which the ultrasonic wavei s propapating. In t h i s a r t i c l e we vresent someof ourpreliminary r e s u l t s .
The a-Li103 single c r y s t a l used i n t h i s investipation was grown from aqueous solu- tion: The orientation of sample was determined by X-ray with an e r r o r not exceeding 0.5 degree. Before the electrodes were apnlied the c r y s t a l was o p t i c a l l y polished t o a f l a t n e s s cf l e s s than a wave length of l i g h t with narallelism l e s s than 30 se- cond of arc. The gold electrode was plated f o r applying e l e c t r o s t a t i c f i e l d on the C direction of c r y s t a l . Sincea-Li103 c r y s t a l i s a polar c r y s t a l , i f the e l e c t r i c f i e l d i s p a r a l l e l t o volar direction, the f i e l d i s called positive, conversely it i s negative.
The ultrasonic frequency uçed f o r attenuation measurement is i n the range of 10-250
CIO-518 JOURNAL DE PHYSIQUE
MHz. The v e l o c i t i e s were measured by "echo overlap method" with frequency a t 10Wz
( 4 ) . The resolution of time measurement i s 0.511s. I I I
-
RESULTSI t was found t h a t when an e l e c t r o s t a t i c f i e l d i s apnlied i n the c direction of a-
~ i I 0 3 c r y s t a l , as welL as an ultrasonic longitudinal wave propagates along the same direction, the attenuation c o e f f i c i e n t of the wave i s increased. The amplitude of successive echoes was found t o be decreased one a f t e r another from the display of oscilloscope. I t was also found t h a t a f t e r the a m l i c a t i o n of the e l e c t r i c f i e l d
,
the attenuation coefficient varies with time, demonstrateing relaxation and f i n a l l y reaching a saturated value as shown i n Fig.1. However, i f the f i e l d is switched o f f , the whole process i s reversed. The decreasing r a t e of amplitude of successive echoes and the number of v i s i b l e echoes from the oscilloscope screen a r e dependent on the e l e c t r i c f i e l d strength and applied t h e .Fig. 1 -The r e l a t i o n between the attenuation coefficient of longitudinal wave and the e l e c t r i c f i e l d vs time along c-direction. The f i e l d is switched on a t 10 mins. and turned o f f a t 40 mins.
The attenuation curves f o r various applied f i e l d strenpth a r e showing i n Fig. 2.
Fig. 2 -The attenuation curves f o r d i f f e r e n t applied e l e c t r o s t a t i c f i e l d strength (E,) vs time t(mins).
O open c i r c l e s --5.3,
closed c i r c l e s --16.0, A oilen t r i a n g l e - - 26.7,
A closed t r i a n g l e --53.4, n open square --266.8, i closed square --533.6V/an.
O 50 100 150
IV - DISCUSSION
' m i
" )a-LiIO? i s a piezoelectric c r y s t a l and has conductivity u a = l x l ~ - 1 4 and oc=3x10- 9
(
n
.cm )-lalong "a" and "c" axis resnectively.
The main c a r r i e r being lithium ion. This indicates that the a-Li103 c r y s t a l exhibits a quasi one dimensional conductivity (5).
The increase i n attenuation coefficient by e l e c t r o s t a t i c f i e l d f o r longitudinal wave i s possibly caused by the coupling between the ultrasonic wave and the mobile ions. But
,
the shear wave cannot prcduce the longitudinal piezoelectric f i e l d i n c direction, then it cannot produce the couplinp between the shear wave and the mobile ions. So t h a t i n t h i s case w i l l not f u r t h e r attenuate the shear wave by e l e c t r i c f i e l d . Furthermore, almost no c a r r i e r c m t r a n s ~ o r t along the a o r b direction, so neither longitudinal wave nor shear wave nronagateing along the a and b direction w i l l f u r t h e r attenuate with applied e l e c t r i c f i e l d on a and b axis. The conductivity oc of a-Li103 i s low, so i t s mobility pp mst be small and there- fore, the c a r r i e r velocity Vp=+Eo, even a t the highest e l e c t r i c f i e l d,
can not surpass the velocity of the lonpitudinal wave.dur in^
t h i s time,
the c a r r i e r s c m notcompletely follow the wave,
so the energy i s l o s t from the wave. Conversely,JOURNAL DE PHYSIQUE
case.
/1/ Yang Zhen, Cheng Yu-Fen, Niu Shi-wen, L i Yin-yuan, Acta Physica Sinica, 24 (1975) ,6.
/ 2 / Yang Hua-guan, Acta Physica, 29 (1980), 1039; 30 (1981),928.
/3/ Zhu Yong
