Characterization of copper bromine boracite Cu3B7O13Br

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Reference

Characterization of copper bromine boracite Cu3B7O13Br

BERSET, Guy Alexis, et al.

Abstract

Dielectric constant, spontaneous polarization, and birefringence have been measured between 10 to 290 K on single domain samples of Cu3B7O13Br.

BERSET, Guy Alexis, et al. Characterization of copper bromine boracite Cu3B7O13Br.

Ferroelectrics, 1988, vol. 79, no. 1, p. 177-180

DOI : 10.1080/00150198808229425

Available at:

http://archive-ouverte.unige.ch/unige:30825

Disclaimer: layout of this document may differ from the published version.

Farodecrrics, 1988, Vol. 79, pp. 177-1&0 Reprints available directly from the publisher Photocopying permitted by license only

© 1988 Gordon an<! Breach Science Publishers S.A.

Printed in the United States of America

CHARACTERIZATION OF COPPER BROMINE BORACITE Cu3B-f)13Br

GUY BERSET+, MARTIAL CLIN+ *,JEAN-PIERRE RIVERA + and HANS SCHMID + + Department of Mineral, Analytical and Applied Chemistry, University of Geneva, CH -1211 Geneva 4, Switzerland.

• Group of phase transitions, University of Picardie, 33 Rue St Leu, 80CXlO Amiens, France.

Abstract Dielectric constant, spontaneous polarization and birefringence have been measured between 10 K to 290 K on single domain samples of Cu3B-f)13Br.

INTRODUCTION

At about 243 K the Cu-Br boracite (Cu3B7013Br) undergoes an rmproper ferroelectric/ferroelastic phase transition from a cubic F43cl to an orthorhombic

-

phase mm22. Up to now, dielectric investigations (spontaneous polarization (P

J

^and

dielectric constant ( € )) have only been performed on polydomain crystaJs3 or by means of point by point techniques4 and have failed to give reliable measurements, in particular near the phase transition. In this paper, dielectric measurements versus temperature of Cu-Br boracite have been re-examined on single domain samples,

-

especially p s and the dielectric constant € 33> the behaviour of which near the ferroelectric transition has been specified. The temperature dependence of the spontaneous birefringence on the three principal sections is also reported.

EXPERIMEN'"! S AND RESULTS

Single crystals were grown by chemical vapour transport. On a (lOO)c cut platelet, semi-transparent gold on chromium electrodes were evaporated, and a field of 13 KV /cm was applied during cooling through the ferroelectric transition in order to yield a ferroelectric single domain. A low frequency impedance analyzer (HP 4192A) connected

[ 177]/471

4721[178] G. BERSET et al.

to a computer for automated data acquisition was used. A preliminary measurement of the capacity of the sample versus frequency at 12 K and 293 K (Fig.1) was realized in order to determine a frequency range where neither piezoelectric resonance nor relaxation mechanism could alter the results. At 100 KHz, €33 has been measured (FJ.&.2) from 11 K to 290 K Values are systematically smaller than previous results3 obtained at 1 KHz4 (also in agreement with Fig.1). At the ferroelectric transition,

€33 shows a discontinuity which corresponds to an upward jump on cooling. This behaviour, also encountered :in certain other boracites, has been discussed5 in the framework of a Landau phenomenological approach using a single six dimensional order parameter related to the X point (k=CXl1r/a) of the cubic phase centered Brillouin

-

zone surface. The temperature dependence of P ₅ has been measured using an electrometer (Keithley 642) (F~&3). The values obtained are about five times higher than those reported for a polydomain sample3. At low temperature, where a ferromagnetic phase transition has been observed at 11 K by means of hysteresis loops6, careful high

-

resolution measurements of Ps have been performed. However, contrary to other ferromagneticjferroelectric boracites7,8, no drastic change of slope was detected (Inset of Fig3). The spontaneous birefringence

fills

of the mm2 phase has been

-

measured on a (100)c cut

Q

P

J

and a (llO)c cut, corresponding to two of the three indicatrix principal sections. The difference in T c of about 10 degrees between (100)c and (llO)c cuts (FJ.&.4) can be attributed to different groMh sectors9. By admitting

-

that

fills Q

P

J

represents

n:y-xu.

in ^analogy to all other known bromine boracites,

fills

of the third section (no available sample) was calculable (FJ.g.4). As can be seen on figure 4, premonitory effects of magnetic ordering seem to affect

.Lns

already at about 60 K Moreover high resolution plot below 20 K (Inset of Fig.4) shows a pronounced minimum, coinciding with the ferromagnetic Curie point. A more detailed report will be given elsewhere.

ACKNOWLEDGEMENTS

The authors are grateful to E. Burkhardt and R. Cros for technical help and the

"Fonds National Suisse de la Recherche Scientifique• (n• 2.081-0.86) for support.

COPPER BROMINE BORACITE [179)1473

40 C(pf) 30

20

10

0

-

1

Cu-8< (100)₀

293 K

/ 12 K

10 100 1000

1V-~.

-'\.----

,...----

10000

1 9 ; - - - -

£,

17

15

13

Cu-Br (100)₀ 100KHz

f (KHz) 11 4--~---.--~---.--~-_j

FIGURE 1 Capacity vs. frequency;

sample (100)₀ thickness 0.040 mm, surface 3.51 mm2_

p (...1!.1'.) Cu- Br

• cm:r

\

(100)

0

2

•

V

1

{I _•

^T(K)

0 10 20 30 40 0

0 100 200 T ( Kl

FIGURE 3 Spontanwus polarization vs. temperature; sample

(1~)

0

^{thickness 0.040}

mm, surface 3.51 mm2.

0 100 200 T ( K)

FIGURE 2 Dielectric constant vs.

temperature at 100 KHz;

sample: (100)c-cut, thickness 0.040

surface 3.51 =2-

10-3

• ⁽¹⁰⁰⁾₀^{-cut .l} P, ^Cu-Br

u

• C10

"

t: • c

~ •

;;

.

^___ (~10lc-cut

I

o"-'l2J

'

• _,. .._,'

^{I I}

0 10 tO T(K)

0 !10 100 1!10 200

T..-perat.ure (KJ

FIGURE 4 Spontanwus birefringence vs. temperature; sample:

(100)₀ thickness 0.122

= ; (llO)c thickness 0.048=.

I ' I I I I I I

474/[180] G. BERSET ~tal.

REFERENCES

1) RJ. Nelmes and W J. Hay, J. Phys. C.li, 5247 (1981).

2) H. Scbmid and H. Tippman.n, fcrroclcctrics. 2Q, 21 (1978).

3) S.N. Drozhdin, B.G. Bochkov, N.D. Gavrilova, T.V. Popova, V .A. Koptsilc and V.K.

Novik, Sov. Phys. Cristallw .. 2Q, 526 (1976).

4) P. Genequand, H. Scb.mid, G. Pouilly and H. Tippmann,

Le

Journal de Physique. ~

287 (1978).

5) P. Toledano, H. Scb.mid, M. Clin and J.P. Rivera, Jap, J. Appl. Phys, 2:1, Suppl 24-2, 347 (1985).

6) G. Berset, J.P. Rivera and H. Scb.mid, unpublished.

7) J.P. Rivera and H. Scb.mid, Ferroelectrics. ~ 295 (1984).

8) M. Clin et al., unpublished.

9) J.F. Rossigno~ J.P. Rivera and H. Scb.mid, Jap. J, Appl. Phys, 2:1, Suppl 24-2, 574 (1985).