A Temperature-Responsive Copper Molybdate Polymorph Mixture near to Water Boiling Point by a Simple Cryogenic Quenching Route

Smart temperature-responsive inorganic materials in accessible temperature ranges open up new positions in the technology. Herein, we present for the first time a CuMoO4 polymorph mixture prepared by a simple cryogenic quenching approach, which offers a fast temperature response close to water boiling temperature for use as a permanent temperature recorder. The new cryogenic quenching technique initiates the formation of a unique polymorph mixture of a deep brown color with a nonuniform combination of gamma- and alpha-CuMoO4, with the gamma phase being confined to the outer region of alpha-CuMoO4, which has been prepared by conventional solid-state synthesis. In situ structural analysis and refinement results confirm the presence of CuMoO4 a and gamma polymorphs in which the amount of gamma polymorph decreases and that of the alpha phase increases with temperature, accounting for the irreversible thermochromic behavior. The thermal analysis reveals that the polymorph mixture exhibits a fast response with the color changing from deep brown to bright green with intermediate colors of light brown, yellowish green, and light green depending on the exposure temperature as observed from reflectance measurements.