For the first time in a bulk proper uniaxial ferroelectrics, double antiferroelectric-like hysteresis loops have been observed in the case of Sn2P2S6 crystal. The quantum anharmonic oscillator model was proposed for description of such polarization switching process. This phenomenon is related to three-well local potential of spontaneous polarization fluctuations at peculiar negative ratio of coupling constants which correspond to inter-site interaction in given sublattice and interaction between two sublattices of Sn2P2S6 modeled crystal structure. Obtained data can be used for development of triple-level cell type memory technology.PACS numbers: 64.60. De,77.80.Dj,77.84.Bw With the development of modern information technology, humanity is needed in ever larger volumes of digital information storage. Due to the fact, that the technological norms for reducing the size of memory cells gradually approach the limitations imposed by physical laws, memory manufacturers are looking for ways out of this situation. One of the methods for increasing the density of information storage is the use of memory cells with several logical states. In such systems, several bits of information are stored in one cell. A vivid example of this approach is a multi-level cell and triple-level cell (TLC) type flash memory [1]. However, flash-technology has a number of drawbacks [2], which leads to the search for new types of memory cells. One of the candidates for the role of the non-volatile universal memory of the future is ferroelectric memory (Fe-RAM) [3]. As it turned out, in these memory cells it is also possible to store several information bits [4]. However, the practical implementation of such systems is only at the level of theoretical calculations.In this Letter we propose the use of a room temperature proper uniaxial ferroelectric-semiconductor Sn 2 P 2 S 6 as an active material of a ferroelectric memory cell. The three-well local potential for the spontaneous polarization fluctuations [5] allows one cell to store three bits of information. This makes it possible to create on its base not only memory cells, but also non-Boolean information systems.In Sn 2 P 2 S 6 crystals the second order phase transition from paraelectric phase (P2 1 /n) into ferroelectric one (Pn) occurs at T 0 ≈ 338 K. At room temperature spontaneous polarization is oriented in (010) monoclinic symmetry plane near [100] direction [6]. Origin of spontaneous polarization is related to Sn 2+ cations electron lone pair stereoactivity together with valence fluctuations P 4+ + P 4+ ←→ P 3+ + P 5+ inside (P 2 S 6 ) 4− anions [5,7,8] which in whole can be considered in frame of second order Jahn-Teller effect [9]. Thermodynamics of this mixed "displacive -order/disorder" continuous transition can be described in the Blume-Emery-Griffiths model [10,11], which consider possibility of thermal fluctuations between three values of pseudospins ("-1", "0", "+1") in local three-well potential. This model predicts possibility of metastable nonpolar states inside of ferro...

Perovskite ceramics of the Bi1-xLaxFe0.5Sc0.5O3 composition (0.30≤x≤0.35) that cannot be sintered in bulk form as a single phase using the conventional ceramic route were successfully prepared using the high-pressure/high-temperature technique. It has been shown that the roomtemperature compositional crossover from the antipolar phase whose incommensurate modulation of displacements of Bi/La and oxygen is described by the Imma(00γ)s00 superspace group to the non-polar Pnma phase occurs in the narrow range between x=0.33 and x=0.34 with no phase coexistence. The features of this compositional crossover are discussed in comparison with that observed in the Bi1-xLaxFeO3 system.

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In this paper we report a dielectric study on four single crystals Pb2P2S6, (Pb0.98Ge0.02)2P2S6, (Pb0.7Sn0.3)2P2S6 + 5% Ge and (Pb0.7Sn0.3)2P2Se6 + 5% Ge down to 20 K. A new quantum paraelectric state was reported in the Ge-doped samples at low temperatures. In all of these materials the non-classical T2 temperature dependences of inverse dielectric permittivity were observed. The dielectric constants of Pb2P2S6-based single crystals were measured between 20 and 300 K. The temperature dependences of dielectric permittivity were analysed on the basis of Barrett’s model as a signature of quantum paraelectricity.

The dipole ordering in Sn(Pb)2P2S(Se)6 materials may be tuned by chemical substitution realizing a ferroelectric quantum phase transition and quantum glassy or relaxor type phenomena on different parts of the phase diagram. The introduction of Ge impurity increases the temperature of the phase transitions and initiates a more pronounced Ising type critical anomaly in the Sn2P2S6 crystal, does not shift the coordinate of the Lifshitz point xLP in Sn2P2(SexS1−x)6 mixed crystals, and induces the appearance of a ferroelectric phase transition in quantum paraelectrics Pb2P2S6 and inhomogeneous polar ordering in (Pb0.7Sn0.3)2P2S(Se)6 crystals. For the Pb2P2S6 crystal, the real part of the dielectric permittivity in the quantum critical regime varies as 1/T2 instead of the expected 1/T3 behavior for uniaxial materials. Such an observation can be partially explained by a screening phenomenon in the semiconductor materials of the Sn(Pb)2P2S(Se)6 system, which weakens the long-range electric dipole interactions, and also provides, at high temperatures, a critical behavior near the Lifshitz point (studied by thermal diffusivity) similar to the one predicted in the case of systems with short-range interactions. At low temperatures, a quantum critical behavior in the Pb2P2S6 crystal can be established by a small amplitude of electric dipoles together with the nonlinear coupling between polar and antipolar fluctuations. An increase in thermal conductivity is induced by Ge impurity in the Pb2P2S6 crystal, which is explained by the weakening of the acoustic phonons resonance scattering by soft optic phonons because of the appearance of ferroelectric phase polar clusters.