Remeasurement of the structure of hexagonal ZnO

Abstract

The X-ray scattering pattern of hexagonal ZnO at 298°K, within a reciprocal lattice hemisphere of radius (sin 0)/2= 1.02 A,-~ containing the polar c* axis as diameter, was measured with PEXRAD. The integrated intensities of 374 reflections, resulting in 141 independent Fracas, were determined. The structure was refined by the method of least squares: the final agreement index R was 0"0378. The sole position parameter is u = 0.3825 + 0.0014. The predicted value is 0.3799, obtained from the measured c/a ratio of 1.602107 and assuming equal Zn-O distances in the ZnO4 tetrahedra. The characteristic Debye temperature O, in isotropically vibrating ZnO, is 370°K. The absolute configuration of the ZnOa tetrahedra is such as to present a triangular oxygen face normal, directed from the face, toward the positive sense of the piezoelectric polarization as induced by a compressive stress applied along the polar axis. The piezoelectric coefficients are predicted to have a small temperature dependence.

Análise teórica da interação de CO, CO2 e NH3 com ZnO

“…A simulação foi desenvolvida utilizando o método semi-empírico AM1, implementado no programa MOPAC 6.0 62 , para a otimização dos parâmetros geométricos. Os modelos foram obtidos a partir dos dados cristalográficos 31 . Os parâmetros geométricos das moléculas de CO, CO 2 e NH 3 foram totalmente otimizados, utilizando o algoritmo Broyden-Fletcher-Goldfarb-Shanno (BFGS) [63][64][65][66] , enquanto que os parâmetros geométricos do "cluster" foram mantidos congelados.…”

“…O ZnO cristaliza-se em uma estrutura hexagonal do tipo wurtizita, na qual cada átomo de zinco está no centro de um tetraedro distorcido coordenado a quatro outros oxigênios vizinhos 31 . Existem três superfícies naturais: a polar terminada em Zn, o plano hexagonal (0001), onde os íons zinco estão posicionados para fora, o plano polar (0001 -) terminado em oxigênio, onde os íons oxigênio estão posicionados para fora e o plano não polar prismático (101 -0) onde ambos, zinco e oxigênio, estão no mesmo plano.…”

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

“…The lattice parameters predicted with the DFT-PBE0 method are in very good agreement with the experimental values for bulk ZnO (a = 3.250 Å and c = 5.207 Å). 39 The difference between the experimental and calculated lattice parameters a/c is +0.5%/+0.1% for the larger TZVP basis set and +0.1%/-0.4% for the smaller SVP basis set. For creating atomic-level models of the ZnO:HQ superlattices, we first had to consider the preferred orientation of ZnO in the ALD/MLD grown superlattices.…”

Simulation of reconstructions of the polar ZnO(0001)surfaces

“…186 in crystallographic tables). 5,6 The structure may be understood as two interpenetrating hexagonal lattices, with each Zn (resp. O) sitting at the centre of a distorted O (resp.…”