Pressure-induced structural phase transition in Zn0.97Al0.03O nanostructure powders under high pressure by angular dispersive X-ray diffraction
Chih-Ming Lin1*, Hsin-Tzu Liu2,3, Shi-Yao Zhong1, Yi-Te Chiu1, Ming-Fong Tai4, Yu-Chun Chuang5, Yen-Fa Liao5
1Department of Applied Science, National Hsinchu University of Education, Hsinchu, Taiwan
2Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan
3Chemical Systems Research Division, Chung-Shan Institute of Science & Technology, Taoyuan, Taiwan
4Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
5National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* presenting author:Chih-Ming Lin,
Plate-like and granular shapes aluminum-doped zinc oxide (AZO) nanostructure powder (NP), Zn0.97Al0.03O, was synthesized using a chemical precipitation method. We used reactants of zinc nitrate and aluminum nitrate as well as urea as the precipitating agent to get precursor. By the thermogravimetric analysis (TGA), precursor was converted to oxide from hydroxide near about 250oC and then heated to 500oC for the temperature of the thermal processes of the precursor species. Then the precursor was calcined at 500oC for three hours. The structure and morphology of the products were measured and characterized by angular dispersive X-ray diffraction (ADXRD) and scanning electron microscopy (SEM). ADXRD results showed that Zn0.97Al0.03O NP exhibited würtzite zinc oxide structure and there was no other impurity phase in the Zn0.97Al0.03O NPs and Al atoms were doped into the zinc oxide lattice by substituting for zinc atoms. The grain size of Zn0.97Al0.03O NP was estimated as 21.4 nm by using the isotropic LX profile term of GSAS. SEM images showed that Zn0.97Al0.03O NP had plate-like and granular shapes. The ⁷high pressure induced phase transition in Zn0.97Al0.03O NP at ambient temperature have been investigated using ADXRD under high pressure up to around 19.2(1) GPa. It can estimate that the transition pressure of the B4-to-B1 phase transformation increases from 9.9 GPa for bulk ZnO to 12.7 GPa for 21.4 nm Zn0.97Al0.03O NP by the surface energy difference between the phases involved. For loading run, in situ ADXRD measurements found that a würtzite(B4)-to-rocksalt(B1) structural phase transition pressure of Zn0.97Al0.03O NP began at 9.0(1) GPa. Compared to the phase-transition pressure (Pt) of 21.4 nm ZnO(12.7 GPa), a reduction of around 3.7 GPa is exhibited. This reduction in phase-transition pressure ΔPt in Zn0.97Al0.03O NP suggests that Zn2+ and Al3+ are mainly found in tetrahedral and octahedral sites might be the source of this reduction.

Keywords: nanostructure powder, angular dispersive X-ray diffraction, high pressure, phase transition, GSAS