Influence of tin substitution on negative thermal expansion of K2Zr2-xSnxP2SiO12 (x = 0 - 2) phosphosilicates ceramics

Abstract

In this research work, compounds of the chemical formula K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1, 1.5, 2) were synthesized by solution method and characterized by powder X-ray diffraction and spectroscopic techniques. Powder XRD analysis revealed that the phase formation temperature vary with the substitution of Sn4+ for Zr4+ at the octahedral site of langbeinite structure. The stretching and bending vibrational modes of PO43− and SiO44− tetrahedra were identified in the region of 407 cm−1 - 1094 cm−1. Thermogravimetric analysis proved that the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12 were thermally stable up to 1000 °C and 650 °C, respectively. Interestingly, negative thermal expansion coefficient was observed for the solid solutions K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2). The average thermal expansion coefficients of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 in the temperature range 30 °C–600 °C were found to be −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C and −1.27 × 10−5/°C, respectively. Coefficient of thermal expansion was increased by the substitution of tin for zirconium. The increase was obvious up to 250 °C and stabilized after 300 °C. The ionic radii, bond strength, structural distortion, density and microstructures were considered to explain the variation in thermal expansion.