Investigation of the anisotropic thermal expansion of PbIn6Te10 crystal by high temperature x-ray diffraction measurements

Abstract

The PbIn6Te10 crystal, a IR laser frequency conversion material, grown via the Bridgman method in a four-zone furnace with dimensions ϕ35mm×90mm, was subject to the investigation of its thermal expansion behavior using high-temperature X-ray diffraction in the range of 25-450 ℃. Based on the obtained data, the average thermal expansion coefficients of 15.21×10-6 K-1 for αa and 6.44×10-6 K-1 for αc were determined utilizing the least square method. The study revealed that the linear and volume thermal expansion coefficients of PbIn6Te10 crystals satisfy the relationships αa﹥αc﹥0, αV =2αa+αc, and αa increased while αc decreased with increasing temperature, accentuating a substantial anisotropy in thermal expansion between the crystal's principal axes. A detailed exploration pinpointed that the variations in the PbTe6 octahedron primarily dictated the fluctuations in the PIT unit cells, with further investigation uncovering its association with variations in the nearest neighboring bonds, which is mainly related to Pb-Te4 and Pb-Te2 bonds. Concurrently, the determination of temperature-dependent anisotropic thermal expansion coefficient α, was complemented by calculating Grüneisen parameter using Quasi-harmonic Debye model. Remarkably, these parameters also exhibited anisotropic behaviors ( increase with temperature wheras decrease, α⊥﹥α∥), contributing additional insights into the crystal's thermal characteristics.