Temperature variation of optical absorption edge in Sn2P2S6 and SnP2S6 crystals

• Published in: Ferroelectrics 2001-01, Vol.254 (1), p.295-310
• Main Authors: Studenyak, I. P., Mitrovcij, V. V., Kovacs, Gy. Sh, Mykajlo, O. A., Gurzan, M. I., Vysochanskii, Yu. M.
• Format: Article
• Language: English
• Subjects: absorption edge; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; layered crystal; Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity); Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; phase transition; Physics; Uniaxial ferroelectric; Urbach rule
• ISSN: 0015-0193; 1563-5112
• DOI: 10.1080/00150190108215009

Temperature variation of the optical absorption edge of Sn 2 P 2 S 6 ferroelectric with three-dimensional crystalline structure and SnP 2 S 6 layered crystals with 2D structure is studied. In both cases the Urbach shape of the absorption edge is revealed, its temperature behaviour in Sn 2 P 2 S 6 crystal being determined by the presence of a ferroelectric phase transition. In Sn 2 P 2 S 6 crystals the exponential parts of the absorption edge plots both in ferroelectric and paraelectric phases have a common convergence point. The anisotropy of the Urbach absorption edge parameters and their temperature variation in the range of the phase transition in Sn 2 P 2 S 6 is studied. The influence of different types of disordering, including 3D→2D transition, on the absorption edge energy position and shape in Sn 2 P 2 S 6 and SnP 2 S 6 crystals is analyzed.