Phase Transition and Negative Thermal Expansion Property of ZrMnMo_3O_12

A novel material of ZrMnMo_3O_12 with negative thermal expansion is presented. The phase transition temperature and coefficient of thermal expansion (CTE) are investigated by temperature-dependent x-ray diffraction and Raman spectra. It is shown that ZrMnMo_3O_12 adopts monoclinic structure with space group P21/a (No. 14) from 298 to 358 K and transforms to orthorhombic with space group Pnma (No. 62) above 363 K. The linear CTE obtained from the results of XRD refinement is -2.80\times10^-6 K^-1 from 363 to 873 K. The CTE of the bulk cylinder ceramic measured by a thermal dilatometer is -4.7\times10^-6 K^-1 from 373 to 773 K approximatively.