Structural Transitions in Nanosized Zn0.97Al0.030 Powders under High Pressure Analyzed by in Situ Angle-Dispersive X-ray Diffraction

Abstract

Nanosized aluminum-doped zinc oxide Zn1-xAlxO (AZO) powders (AZO-NPs) with x = 0.01, 0.03, 0.06, 0.09 and 0.11 were synthesized by chemical precipitation method. The thermogravimetric analysis (TGA) indicated that the precursors were converted to oxides from hydroxides near 250 degrees C, which were then heated to 500 degrees C for subsequent thermal processes to obtain preliminary powders. The obtained preliminary powders were then calcined at 500 degrees C for three hours. The structure and morphology of the products were measured and characterized by angle -dispersive X-ray diffraction (ADXRD) and scanning electron microscopy (SEM). ADXRD results showed that AZO-NPs with Al content less than 11% exhibited wurtzite zinc oxide structure and there was no other impurity phase in the AZO-NPs, suggesting substitutional doping of Al on Zn sites. The Zn0.97Al0.030 powders (A3ZO-NPs) with grain size of about 21.4 nm were used for high-pressure measurements. The in situ ADXRD measurements revealed that, for loading run, the pressure-induced wurtzite (B4)-to-rocksalt (B1) structural phase transition began at 9.0(1) GPa. Compared to the predicted phase-transition pressure of 12.7 GPa for pristine ZnO nanocrystals of similar grain size (similar to 21.4 nm), the transition pressure for the present A(3)ZO-NPs exhibited a reduction of 3.7 GPa. The significant reduction in phase -transition pressure is attributed to the effects of highly selective site occupation, namely Zn2+ and Al3+, were mainly found in tetrahedral and octahedral sites, respectively.