Preparation of Zr(Mo,W)O with a Larger Negative Thermal Expansion by Controlling the Thermal Decomposition of Zr(Mo,W)(OH,Cl)∙2HO

Solid solutions of Zr(Mo,W)O(OH,Cl)∙2HO with a preset ratio of components were prepared by a hydrothermal method. The chemical composition of the solutions was determined by energy dispersive X-ray spectroscopy (EDX). For all the samples of ZrMoWO(OH,Cl)∙2HO (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2.0), TGA and in situ powder X-ray diffraction (PXRD) studies (300-1100 K) were conducted. For each case, the boundaries of the transformations were determined: Zr(Mo,W)O(OH,Cl)∙2HO → orthorhombic-ZrMoWO (425-525 K), orthorhombic-ZrMoWO → cubic-ZrMoWO (700-850 K), cubic-ZrMoWO → trigonal-ZrMoWO (800-1050 K for x > 1) and cubic-ZrMoWO → oxides (1000-1075 K for x ≤ 1). The cell parameters of the disordered cubic-ZrMoWO (space group Pa-3) were measured within 300-900 K, and the thermal expansion coefficients were calculated: -3.5∙10 - -4.5∙10 K. For the ordered ZrMoWO (space group P23), a negative thermal expansion (NTE) coefficient -9.6∙10 K (300-400 K) was calculated. Orthorhombic-ZrW2O is formed upon the decomposition of ZrWO(OH,Cl)∙2HO within 500-800 K.