Average and Local Crystal Structures of (Ga_1-xZn_x)(N_1-xO_x) Solid Solution Nanoparticles

We report a comprehensive study of the crystal structure of (Ga_1-xZn_x)(N_1-xO_x) solid solution nanoparticles by means of neutron and synchrotron X-ray scattering. In our study, we used four different types of (Ga_1-xZn_x)(N_1-xO_x) nanoparticles, with diameters of 10-27 nm and x = 0.075-0.51, which show energy band gaps from 2.21 to 2.61 eV. Rietveld analysis of the neutron diffraction data revealed that the average crystal structure is hexagonal wurtzite (space group P6₃mc) for the larger nanoparticles, while the crystal structure of smaller nanoparticles is disordered hexagonal. Pair-distribution-function analysis found that the intermediate crystal structure retains a "motif" of the average one; however, the local structure is more disordered. The implications of disorder on the reduced energy band gap are discussed.