Ukrainian Journal of Physical Optics 

Beley L.M., Mykajlo O.A., Stephanovych V.O., Studenjak I.P., Gurzan M.I. and Vysochanskii Yu.M.

The temperature and concentration dependences of Raman scattering and optical absorption spectra for CuInP₂(Se_xS_1-x)₆ crystals are investigated. Similarly to dynamic disordering of Cu⁺ ions at the transition from ferrielectric into paraelectric phase for CuInP₂S₆  compound, static disordering of these ions in the mixed crystals in the dipole glassy state at low temperatures determines rise in the phonon damping and increase in the energetic width w of exponential optical absorption edge. The concentration and temperature dependences w(T,x) clearly reveal “asymmetry” of the dipole ordering on T–x phase diagram: the dipole glassy state smoothly evolves into ferrielectric one, coexisting with the latter under decrease of selenium content till x = 0.  The dipole glassy state sharply transforms into ferrielectric phase with growing selenium concentration, passing through the relaxor state in the region of x = 0.7–0.8.

Keywords: ferrielectrics, dipole glass, CuInP2S(Se)6, Raman scattering, optical absorption

PACS: 77.80.Bh, 78.40.Ha, 61.82.Fk, 78.40.Fy, 78.40.Pg 
Ukr. J. Phys. Opt. 8 13-24  doi: 10.3116/16091833/8/1/13/2007
Received: 20.01.2007 

REFERENCES
1. Simon A, Ravez J, Maisonneuve V, Payen C and Cajipe V, 1994.Paraelectric-ferrielectric transition in the lamellar thiophosphate CuInP2S6. Chem. Matter. 6: 1575 - 1582.
        doi:10.1021/cm00045a016  http://dx.doi.org/10.1021/cm00045a016
2. Bourdon X, Maisonneive V, Cajipe V, Payen C and Fischer J, 1999. Copper sublattice ordering in layered CuMP2Se6 (M = In, Cr). J. of Alloys and Compounds. 283: 122 - 127.
        doi:10.1016/S0925-8388(98)00899-8  http://dx.doi.org/10.1016/S0925-8388(98)00899-8
3. Maisonneuve V, Cajipe V, Simon A, Von Der Muhll and Ravez J, 1997. Ferrielectric ordering in lamellar CuInP2S6. Phys. Rev. B. 56: 10860 - 10868.
        doi:10.1103/PhysRevB.56.10860  http://dx.doi.org/10.1103/PhysRevB.56.10860
4. Fagot-Revurat Y, Bourdon X, Bertran F, Cajipe V and Malterre D, 2003. Interplay between electronic and crystallographic instabilities in the low-dimensional ferroelectric CuInP2Se6 J. Phys.: Condens. Matter. 15: 595 - 602.
        doi:10.1088/0953-8984/15/3/323  http://dx.doi.org/10.1088/0953-8984/15/3/323
5. Rushchanskii KZ, Vysochanskii YuM, Cajipe VB and Bourdon X, 2006. . Influence of pressure on the structural, dynamical and electronic properties of the SnP2S6 layered crystal. Phys. Rev. B. 73: 115115 - 115126.
        doi:10.1103/PhysRevB.73.115115  http://dx.doi.org/10.1103/PhysRevB.73.115115
6. Vysochanskii YuM, Stephanovich VA, Molnar AA, Cajipe VB and Bourdon X, 1998. Raman spectroscopy of the CuInP2S6 and SnP2S6 crystals lattice vibrations. Phys. Rev. B. 58: 9119 - 9124. 
        doi: 10.1103/PhysRevB.58.9119   http://link.aps.org/abstract/PRB/v58/p9119
7. Studenyak IP, Mitrovcij VV, Kovacs GySh, Gurzan MI, Mykajlo OA, Vysochanskii YuM and Cajipe VB, 2003. Disordering effect on optical absorption processes in CuInP2S6 ferroelectrics. Phys. Status Solidi (b). 263: 678 - 686.
        doi:10.1002/pssb.200301513  http://dx.doi.org/10.1002/pssb.200301513
8. Studenyak IP, Mykajlo OA, Stephanovich VO, Gurzan MI, Vysochanskii YuM and Cajipe VB, 2003. Phase transitions and optical absorption edge in layered ferrielectrics CuInP2Se6. Phys. Stat. Sol. (a). 198: 487 - 494. 
        doi:10.1002/pssa.200306637  http://dx.doi.org/10.1002/pssa.200306637
9. Vysochanskii YuM, Molnar AA, Gurzan MI, Cajipe VB and Bourdon X, 2000. Dielectric measurement study of lamellar CuInP2Se6: Successive transitions towards a ferroelectric state via an incommensurate phase. Solid State Commun. 115: 13 - 17.
        doi:10.1016/S0038-1098(00)00131-9  http://dx.doi.org/10.1016/S0038-1098(00)00131-9
10. Vysochanskii YuM, Molnar AA, Gurzan MI and Cajipe VB, 2001. Phase transitions in CuInP2(SexS1-x)6 layered crystals. Ferroelectrics. 257: 147-154.
        doi: 10.1080/00150190108016294
11. Vysochanskii Yu, Beley L, Perechinskii S, Gurzan M, Molnar O, Mykajlo O, Tovt V and Stephanovich V, 2004. Phase transitions and disordering effects in CuInP2S(Se)6 layered ferrielectrics. Ferroelectrics. 298: 361 - 366.
        doi:10.1080/00150190490423877  http://dx.doi.org/10.1080/00150190490423877
12. Maior MM, Vrabel VT, Prits IP, Korda NF, Gurzan MI and Vysochanskii YuM, 2005. Dielectric properties of CuInP2(SexS1?x)6 solid solutions. Physics of the Solid State. 47: 1734-1739.
        doi:10.1134/1.2045360  http://dx.doi.org/10.1134/1.2045360
13. Banys J, Grigalaitis R, Macutkevic J, Brilingas A, Samulionis V, Grigas J and Vysochanskii Yu, 2005. Dipolar glass behaviour in mixed CuInP2(S0.7Se0.3)6 crystals. Ferroelectrics. 318: 163 - 168.
        doi:10.1080/00150190590966405  http://dx.doi.org/10.1080/00150190590966405
14. Vysochanskii YuM, Maior MM, Belej LM and Khoma MM, 2006. Phase transitions and relaxational dynamics in layered ferrielectrics CuInP2(SexS1-x)6. In Abstract Book of 4th French and Ukrainian meeting on ferroelectricity. Amiens, 21 – 24 November, 2006.
15. Vysochanskii Yu, Yevych R, Beley L, Stephanovich V, Mytrovcij V, Mykajlo O, Molnar A and Gurzan M, 2003. Phonon spectra and phase transitions in CuInP2(SexS1-x)6 ferrielectrics. Ferroelectrics. 284: 161 - 173.
        doi:10.1080/00150190390204808  http://dx.doi.org/10.1080/00150190390204808
16. Urbach F, 1953. The Long-Wavelength Edge of Photographic Sensitivity and of the Electronic Absorption of Solids. Phys. Rev. 92: 1324.
        doi:10.1103/PhysRev.92.1324  http://dx.doi.org/10.1103/PhysRev.92.1324

(c) Ukrainian Journal of Physical Optics