Negative thermal expansion and shift in phase transition temperature in Mo-substituted ZrW2O8 thin films prepared by pulsed laser deposition

Mo-substituted ZrW₂O₈ (ZrW_1.1Mo_0.9O₈) thin films have been deposited on quartz substrates by the pulsed laser deposition (PLD) method. The effects of oxygen pressure, substrate temperature and annealing temperature on the morphologies and phase compositions of the ZrW_1.1Mo_0.9O₈ thin films were systematically investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The negative thermal expansion and shift in phase transition temperature in cubic ZrW_1.1Mo_0.9O₈ thin films were characterized using high temperature X-ray diffraction. The results indicate that as-deposited ZrW_1.1Mo_0.9O₈ thin films show amorphous phases. Crystallized cubic ZrW_1.1Mo_0.9O₈ thin films were prepared by heating at 1050 °C for 7 min. The growth of the ZrW_1.1Mo_0.9O₈ thin films was strongly influenced by the substrate temperature and oxygen pressure. The ZrW_1.1Mo_0.9O₈ thin film deposited at 500 °C with an oxygen pressure of 10 Pa was smooth and compact, and its thickness was about 720 nm. The high temperature X-ray diffraction analyses demonstrated that the cubic ZrW_1.1Mo_0.9O₈ thin film exhibited strong negative thermal expansion and its thermal expansion coefficient was calculated to be −8.65×10⁻⁶ K⁻¹ from 100 °C to 600 °C. The substitution of Mo in ZrW₂O₈ thin film leads to a remarkable decrease in phase transition temperature, with the α to β structure phase transition occurring below 100 °C. However, with increased testing temperature, the substitution results in part of the cubic ZrW_1.1Mo_0.9O₈ thin film gradually changing into a trigonal phase.