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

Abstract

Mo-substituted ZrW2O8 (ZrW1.1Mo0.9O8) 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 ZrW1.1Mo0.9O8 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 ZrW1.1Mo0.9O8 thin films were characterized using high temperature X-ray diffraction. The results indicate that as-deposited ZrW1.1Mo0.9O8 thin films show amorphous phases. Crystallized cubic ZrW1.1Mo0.9O8 thin films were prepared by heating at 1050°C for 7min. The growth of the ZrW1.1Mo0.9O8 thin films was strongly influenced by the substrate temperature and oxygen pressure. The ZrW1.1Mo0.9O8 thin film deposited at 500°C with an oxygen pressure of 10Pa was smooth and compact, and its thickness was about 720nm. The high temperature X-ray diffraction analyses demonstrated that the cubic ZrW1.1Mo0.9O8 thin film exhibited strong negative thermal expansion and its thermal expansion coefficient was calculated to be −8.65×10−6K−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 ZrW1.1Mo0.9O8 thin film gradually changing into a trigonal phase.