The results of the search for dopants to optimize the ferroelectric phase transition temperature and pyroelectric and piezoelectric properties of Sn(2)P(2)S(6) crystals are reported. Among all dopants only germanium causes a pronounced shift of the phase transition toward higher temperatures. The highest Curie temperature achieved by Ge doping is as high as 88 degrees C. The major advantage of the Ge-doped crystals as compared to pure Sn(2)P(2)S(6) is that the hydrostatic piezoelectric and pyroelectric response is kept high in a wider temperature range with much lower temperature dependence. The effects of the doping on pyroelectric and piezoelectric properties, characterizing the sensitivity of the material to thermal and hydroacoustic excitation, are discussed.

International audienceIn this work we report results on electro-physical, optical and photorefractive investigations for Sb-doped Sn2P2S6 crystals. The crystals are obtained by two methods: the vapour-transport technique and the Bridgman technique using stoichiometric Sn2P2S6 composition with different amounts of antimony in the initial compound. The good optical quality of the crystals obtained with the Bridgman technique is underlined. The dependences of the photorefractive two-beam coupling coefficient and the grating build-up time are investigated at the wavelength of 633 nm. It is found that the sample doped with 1.5% of Sb is characterized by an optimal combination of the main photorefractive parameters exhibiting a fairly high two-beam coupling coefficient (up to 20 cm-1) and a short response time (1.3 ms) that is the shortest among all the previously studied Sn2P2S6 crystals in the red spectral region

Dielectric properties of CuInP 2 S 6 layered crystals in the range of ferrielectric phase transition are studied under hydrostatic pressure. The pressure dependence of the phase transition temperature testifies to the phase transition being of the order/disorder type. The (p, T ) phase diagram of CuInP 2 S 6 crystals has been constructed.

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Nanometric Sn2P2S6 crystalline powders and ceramics are studied by x-ray diffraction and Raman spectroscopy. The average crystallite size is estimated from TEM and x-ray data. The observed features in the Raman spectra are discussed in view of confinement-related selection rules relaxation, surface phonon modes and possible partial substitution of sulfur by oxygen at the nanometric powder surface.