Electronic structure ofSn2P2S6<

Abstract

The electronic properties of the ferroelectric compound Sn 2 P 2 S 6 are investigated by x-ray photoelectron spectroscopy and soft x-ray fluorescence spectroscopy. Excellent agreement between theoretical calculations and experimental data for the electronic structure of the investigated compound is achieved. With help of the Sn core level spectra it is confirmed that the compound contains Sn 2ϩ ions. The valence band mainly consists of five resolvable bands between 3.3 eV and 14.5 eV. Consistent with the results of band-structure calculation and the soft x-ray fluorescence spectra, Sn 2 P 2 S 6 can be viewed as an ionic crystal, built of Sn 2ϩ and the (P 2 S 6 ) 4Ϫ fragments. Within the latter, P-P and P-S bonds are largely covalent and characterized by sp hybridization.

X-ray photoelectron spectroscopy of Sn_2P_2S_6 crystals

“…Above −25 eV there dominate P 3s with mixture of S 3s states. The five experimental bands at −3.3 eV, −7.2 eV, −9.7 eV, −11.5 eV and −14.5 eV are in good agreement with [4].…”

“…The VB consists of five distinguishable bands with the maximum intensity at 2.8 eV, 6.7 eV, 9.2 eV, 11.0 eV, and 14.0 eV. In FE phase the energies are shifted by approximately 0.5 eV to higher values and coincide with those obtained in [4]. In the PE phase, the VB is separated by a gap of about 1.1 eV from the Fermi level.…”

“…The electron density from Sn goes primarily to the neighboring S atoms, yielding nearly full occupation of the S 3p band. The calculated PDOS in this approach slightly differs from the FLAPW calculations [4]. However, the main VB features are the same.…”

“…Electronic structure of Sn 2 P 2 S 6 was studied by X-ray photoelectron and X-ray fluorescence spectroscopes in combination with the full-potential linearized augmented plane-wave (FLAPW) band-structure calculations only in FE phase [4]. Due to a relative complexity and low symmetry of the crystal, one can expect different XPS from different crystal planes (as in SbSI [2]) as well as in PE and FE phases.…”

Annealing-induced formation of Sn2P2S6 crystallites in As2S3-based glass matrix

“…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.…”