Abstract:The Crystal Structure of Sn2P 2S6 G. T hiophosphate, C rystal S tru ctu re
D i t t m a r u n d H e r b e r t S cThe crystal stru ctu re has been determ ined for one of th e monoclinic modifications of Sn2P 2S6. There are P 2S6-groups in th e stru ctu re w ith nearly u n d isto rted point group summ etry 3m. These are connected to a threedim ensional netw ork by 7-fold and 8-fold coordi nated tin-atom s. The crystallographic d a ta of th e cell are: a0 = 9.378(5) Ä, b0 =7.488(5) Ä, c0 = 6.513(5) A, ß = 91,15°(5… Show more
It has been shown experimentally that the ferroelectric nano-particles, in common with other molecular additives, shift the clearing temperature, Tc, extending or reducing the two-phase coexistent region and changing the average order parameter of the single-component nematics. An increase of up to 11 • C or a smaller decrease of as much as 3 • C of Tc, and corresponding changes of the order parameter were observed. In all cases the order parameter of the colloid followed the universal temperature behaviour, which is a characteristic of LCs with molecular additives.
It has been shown experimentally that the ferroelectric nano-particles, in common with other molecular additives, shift the clearing temperature, Tc, extending or reducing the two-phase coexistent region and changing the average order parameter of the single-component nematics. An increase of up to 11 • C or a smaller decrease of as much as 3 • C of Tc, and corresponding changes of the order parameter were observed. In all cases the order parameter of the colloid followed the universal temperature behaviour, which is a characteristic of LCs with molecular additives.
“…In the calculations there have been used the structural data for Sn 2 P 2 S 6 crystals (in the PE (T = 383 K) and FE (T = 293 K) phases) and Sn 2 P 2 Se 6 crystals (in the PE (T = 293 K) phase) taken from [21,33,40] works. The crystals under research are referred to ion-covalent compounds.…”
Section: Methodsmentioning
confidence: 99%
“…The given facts allow us to admit the possible presence of the longitudinal component in the polarization wave in its IC phase. While choosing the elementary cell in accordance with [21], the [100] and [001] axes are orientated at approximately the angle of 91.16…”
Section: Introductionmentioning
confidence: 99%
“…LP coordinates, the polaron peculiarities manifestation in the kinetic properties) testifies to the probably essential connection of the polarization fluctuation with the ions charged state in Sn 2 P 2 S(Se) 6 crystals. Their structure is ion-covalent with two formula units in the elementary cell and nominal chargers of Sn 2+ cations and [P 2 S(Se) 6 ] 4− anions [21,33]. It is possible to assume that under heat displacements of the tin atom sublattice in relation to the quasimolecular complex sublattice and relative displacement of these structural groups as well as their deformations (the pointed out atom displacements in the elementary cell are evidently components of the spontaneous polarization which appears in the FE phase) there also takes place a recharging of ions.…”
Polarizable ion model was used in describing the lattice dynamics in the Sn 2 P 2 S 6 and Sn 2 P 2 Se 6 ferroelectric crystals and their solid solutions. There has been obtained a good agreement of the calculated phonon spectra with the experimental data of Raman and Brillouin spectroscopies, neutron scattering and ultrasound experiments. Paraelectric phase instability has been modelled by negative charge transferring from the tin cations to the chalcogen ions, and by increasing the polarizabilities of the latter. The ferroelectric phase has been stabilized by tin atom displacement from centrosymmetric positions and a partial reversal recharging between tin and chalcogen ions. The effective charges decreasing by moving from Sn 2 P 2 S 6 to Sn 2 P 2 Se 6 compounds determine the shift of condensation wave vector of soft optic phonons in paraelectric phase from q = 0 in sulfur compound to q > 0 in selenium compound. Such a change of dynamical instability character is connected with the appearance of incommensurate phase in Sn 2 P 2 (SexS 1−x ) 6 solid solution under x > 0.28. The "two-mode" instability emerged as possible in the vicinity of Lifshitz point -there have been modelled the condensation of soft optic mode with q ≈ 0 and mixed optic and transversal acoustic phonons near q > 0. This fact requires further experimental and theoretical investigations.
“…At ambient pressure, the Sn 2 P 2 S 6 crystal undergoes a second-order structural transition from the ferroelectric phase (Pn) to the paraelectric (P2 1 /n) one at 337 K, which was thoroughly investigated by X-ray diffraction [5], dielectric studies [6], Raman scattering [7][8][9], inelastic neutron scattering [10], ultrasonic measurements [11], optical spectroscopy [12], birefringence measurements [13], Mössbauer spectroscopy [14,15], X-ray photoelectron spectroscopy [16,17], soft X-ray fluorescence spectroscopy [16], and thermal expansion studies [18]. In most cases, these studies were carried out for good quality bulk single crystals.…”
Abstract. Sn-As-P-S glasses were obtained using co-melting of pre-synthesized As 2 S 3 and Sn 2 P 2 S 6 . Their structure and composition were confirmed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and micro-Raman scattering. Crystallization of Sn 2 P 2 S 6 crystallites from the glass matrix is observed at annealing under relatively low temperatures (410…580 K).
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