Mössbauer ¹¹⁹Sn and XPS spectroscopy of Sn₂P₂S₆ and SnP₂S₆ crystals

Abstract

The monoclinic Sn2P2S6 and rombohedral layered SnP2S6 crystals have been investigated by 119Sn Mössbauer and X‐ray photoelectron spectroscopies. By comparing the isomer shift, quadrupole splitting and binding energies for Sn 3d and 4d core levels in these crystals with such parameters for the metal tin and for different tin compounds it was found that in the Sn2P2S6 crystals Sn existed in the Sn2+ oxidation state and in the SnP2S6 crystals – in the Sn4+ state. Temperature dependences of the isomer shift and Debye–Waller factor satisfied the Debye model in the temperature interval of 6 – 300 K for the SnP2S6 crystals but deviated from such behavior at T > 250 K for Sn2P2S6 crystals. This peculiarity together with specific character of the temperature dependence of the quadrupole splitting were related to the role of the stereoactive Sn 5s2 lone pair electrons in the determined by three‐well potential mechanism of the second order ferroelectric phase transition at 337 K in Sn2P2S6 crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Relaxor behavior and electrothermal properties of Sn- and Nb-modified (Ba,Ca)TiO3 Pb-free ferroelectric

“…Peaks P 1 and P 3 correspond to Sn 21 , and peaks P 2 and P 4 correspond to Sn 41 . All of these closely match the reference energies obtained from SnO and SnO 2 [46,47]. From peak fitting analysis of XPS data, we estimate close to equal concentration of Sn 21 and Sn 41 (Sn 21 :Sn 41 5 0.57:0.43).…”

Ferroelectricity in (PbySn1−y)2P2S6 mixed crystals and random field BEG model

“…13) can be explained in the following way. On substitution of sulfur by selenium, intercell interaction becomes weaker as a result of the stronger covalence of the chemical bonds [24,25], but the stereoactivity of the Sn 2+ cations and the form of the local potential obviously remain almost unchanged. These factors, mostly the intercell interaction weakening, determine the secondorder PT temperature decrease until the TCP is reached.…”

Electronic Structure and Phase Transition in Ferroelectic Sn2P2S6 Crystal

“…Structural evidences of the tin cation stereoactivity was also analyzed in details by structure refinement of the paraelectric and the ferroelectric phases for Sn 2 P 2 Se 6 selenide analog [15]. Through the Mössbauer effect investigations for the 119 Sn nucleus [16] and the NMR spectroscopy for isotopes 31 P and 119 Sn [17,18], the important changes of chemical bonding at the ferroelectric phase transition in Sn 2 P 2 S 6 were found. The X-ray photoelectron spectroscopy confirms growth of the chemical bonds covalence in the ferroelectric phase [19].…”