Ab initiodescription of heterostructural alloys: Thermodynamic and structural properties ofMgxZn1−xOand

André Schleife¹,

M. Eisenacher²,

Claudia Rödl³

et al.

Abstract

Pseudobinary heterostructural alloys of ZnO with MgO or CdO are studied by composing the system locally of clusters with varying ratio of cations. We investigate fourfold (wurtzite structure) and sixfold (rocksalt structure) coordination of the atoms. By means of density functional theory we study a total number of 256 16-atom clusters divided into 22 classes for the wurtzite structure and 16 classes for the rocksalt structure for each of the alloy systems. The fraction with which each cluster contributes to the alloy is determined for a given temperature T and composition x within (i) the generalized quasi-chemical approximation, (ii) the model of a strict-regular solution, and (iii) the model of microscopic decomposition. From the cluster fractions we derive conclusions about the miscibility and the critical compositions at which the average crystal structure changes. Thermodynamic properties such as the mixing free energy and the mixing entropy are investigated for the three different statistics. We discuss the consequences of the two different local lattice structures for characteristic atomic distances, cohesive energies, and the alloys' elasticities. The differences in the properties of Mg x Zn 1−x O and Cd x Zn 1−x O are explained and discussed.

Electronegativity calculation of bulk modulus and band gap of ternary ZnO-based alloys

“…(1) and (2) [3,6,7,9,[23][24][25][26][27], which are consistent with our calculations. From the figures, we found that both bulk modulus and band gap of these alloys with rocksalt structure are larger than those with wurtzite structure.…”

“…Alloying ZnO with other group-II metal oxides, the ternary alloys may possess band gap ranging continuously from about 2.3 to 10.6 eV through changing the dopant concentration. Much theoretical and experimental work has been carried out to investigate the ternary ZnObased alloys including Be x Zn 1Àx O, Mg x Zn 1Àx O, Ca x Zn 1Àx O and Cd x Zn 1Àx O [3][4][5][6][7][8], whose optoelectronic properties have been extensively studied. For Mg x Zn 1Àx O, Ca x Zn 1Àx O and Cd x Zn 1Àx O, the structure phase separation will occur in some transition concentration due to the large crystal structure mismatch between wurtzite ZnO and rocksalt MgO, CaO and CdO.…”

Distribution of cations in wurtzitic InxGa1−xN and InxCarvalho1, Schleife2, Furthmüller3 et al. 2012Phys. Rev. B251180View full textAdd to dashboardCite

“…Due to the point-group symmetry of wz, the total number of 2 n = 256 clusters is grouped into J + 1 = 22 classes. 40,43 A complete treatment of all classes of larger clusters, e. g. of 32-atom clusters with n = 16 would increase the CPU time too much because of the 2 n = 65 536 clusters needed to study. The 16-atom cell can be constructed in such a way that N atoms occupy the top and bottom surfaces of the cell (cf.…”

“…(1) and (2) depend on the average composition x of the alloy as well as the temperature T , hence, it is possible to account for the influence of different preparation conditions. 43 In this work, three situations are distinguished:…”

“…21,43 The excess energy ∆ε j of cluster j is defined with respect to the total energies of the binary end components ε 0 and ε J as…”