Effects of substrate temperature and oxygen pressure in pulsed laser deposited ZrW1.5Mo0.5O8 thin films

ZrW1.5Mo0.5O8 thin films were deposited on quartz substrates by a pulsed laser deposition (PLD) method at various temperatures from room temperature to 500 °C and different oxygen pressures from 5 Pa to 20 Pa. The effects of substrate temperature, ambient O2 pressure on the phase composition, growth and surface morphology of the ZrW1.5Mo0.5O8 thin films were investigated using the X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The negative thermal expansion property and phase transition in cubic ZrW1.5Mo0.5O8 thin film were characterized using high temperature X-ray diffraction (HTXRD). The XRD studies indicated that the as-deposited ZrW1.5Mo0.5O8 thin films showed amorphous phase regardless of O2 pressures and substrate temperatures. Crystallized cubic ZrW1.5Mo0.5O8 thin film was prepared after annealing at 1180 °C for 7 min. The AFM studies showed that the root mean square (RMS) roughness values of the ZrW1.5Mo0.5O8 thin films decreased from 13.557 nm to 4.184 nm. This corresponded with increasing substrate temperature from room temperature to 500 °C. The RMS roughness values increased from 2.526 nm to 7.231 nm with increasing O2 pressures from 5 Pa to 20 Pa. The HTXRD analyses demonstrated that the cubic ZrW1.5Mo0.5O8 thin film exhibited strong negative thermal expansion and its average thermal expansion coefficient was calculated to be −7.7×10−6 K−1 in the temperature range from 30 °C to 600 °C.