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

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 degrees C and 650 degrees 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 degrees C-600 degrees C were found to be -7.01 x 10-6/degrees C, -4.96 x 10-6/degrees C, -1.08 x 10(-5)/degrees C, -1.53 x 10(-5)/degrees C and -1.27x10(-5)/degrees C, respectively. Coefficient of thermal expansion was increased by the substitution of tin for zirconium. The increase was obvious up to 250 degrees C and stabilized after 300 degrees C. The ionic radii, bond strength, structural distortion, density and microstructures were considered to explain the variation in thermal expansion.