NQR investigation of halogenate crystals under pressure

81

Previaus

stludies oi halogenate

crys%als

frave been concerned

with investigating Eerr~-~ piezuf ppo&lectrLc-, eix. properties and far this reason the investigation of the intracrystalline field sy=mmetry and lattice dynamic are of interest especially near 127 the phase transition. In this paper, the I nteif332 ~~~~r~~~~e resonance (NQRI speckra of the, RIU3# NaX03j, NE43C13 and BLQ3 crystals were studied in temperature and pressure ranges 4,2 to 127 300K and 0 tb 5 kbar respectivefy, and the I NQR spectrm of the or-DX03 crystal was investigated at 77X.

82 atoms LntheKI03 crystal lattice. In this case the HI03molecules do not This assumption egrees with fact that the intensity of the form. 'BimpuritylU line (2) of the l&JR spectrum varied in proportion to the impurity concentration. The change of the RQR spectrum multiplicity

990,o

985,O

I

40

Pig. 1. The temperature mixed Ii103 monocrystsl, 1201;

1

I

720

dependence of the e2Qq constant: a) for b) for chemically pyrezziiIC3 polycrystal.

(Pig. la) in mixed XI03 crystals is caused by ordering of impurity protons in the asymmetrical two-minimum potential. For examiaetion of this assump-tion the pressure depertdence of the lg71 EQR frequency (f-3/2+@25/2) was measured in the XIX3 single cryof tile %CR spectrum multiplist3z.lsample (~~i;r.23~). The temperature increase city changing decreases with of the applied pressure up change was to -l,5 lcber. I@ should be noted, that the multiplicity accompa~~ad~y the redist~bution of the EQR lines relative integral i1lten.sity. Thus it is possible to obtain a phase diagram eorresponding to tile p&se dingraT observed in ferroelectrie KDP-type crystcls (ref. 1). potential changes iYe assumed that tlhe shape of the tso-minimu! increase wit:1 02 Iiycirostetic pressure. Herewith the value of the proton tunnel r~~trix element increzzsed, In this case the pressure dependence of tile phase transition temperature point idT,/dP*--w ?ken P -I 1,5 Icbcs) became clear. at

83

298.0

296,O 1

2

3P,kbar

0,5

1,5 P,kbar

,r..- , ‘> (23/2* a) The pressure dependence of t'he lz71 KJR frequencea G 2572) of the (1) end (2) lines for the RIO crystal for different temperatures: 1 - (4,2=2O)K, 2 - 40X, 3 - G01L34 - 77K, 5 - 9OIC, 6 120x 9 - 1301:. b) The pressure dependence of 11oi; 8 ;h~","%s~ transiiion-(e*d) temperature point for the RIO3 crystal. 2’ i

CL-EIOJ, at-KC0 , XaIO3 and UH IO crystals The pressure dependences of the e LOq zz constant and the esymmetlsy pclrezieter2 for the EaIO3 end NH4103 crystals indicate the decreasin=; of the intracrystzl field symmetry in contrast to that for a-III0 3 crystal (Fig. 3). In the case of oL-RIO3 l/qyy - dqyy/dP
The compressibility factor)e (X = l/V - dV/dP, V is volume) for the CA -X0, crystal was estimated using obtained R value variation 1o-6 kbar-I). (X= ( 13, gJL

3j

.

5%

7

43,o

42,5

1

2

3

P,kbar

3ig. 3.The pressure (at P = 40K) metry prrsmeter 2 for the &-RIO. It is knovm um

that

the isotopic

to O-H

DIO-, crystal

length

our experimental datE = 43,457; and 21 &-RIO

substitution

1271

of proton

of the hydrogen

increasing

tals (lef. 3). The increasing crystal must lead to decreasing of t for

of the

bond of the 0 . ..D bond length

ler-dsJ e.s ~1.ruleJto

pzriaion

3

dependences crystal.

in the must Tfor

be

of O-D

covalent

aL-III03 crystal. lerger

both

than

crystals

that

are

bond

EFG

by

asym-

deuteri-

length in crysin d-D103 length

Therefore,

in the

comvalue

for aC-EII03. Really equal:

&DI03

=

= 43,365; at 77K. 3

and A.ntiferroelecB. Zeks, Soft Xodes in Ferroelectrics tries, Amsterdam, 1974, p.228. V.P. Zenchenko, D.Z. Baisa, -4.1. Barabash et al., Physical and

R. Blinc,

Liethemztical IJethods in Coordination Chemestry, Proceedings of the VI ill-Union Conference, Kishinev, 1977, p. 105. G.C. Pirnentel, A.L. SicClellan, The Hydrogen Bond, San Francisco, London, 1960, p.222.