Theoretical Study on the Origins of the Gap Bowing in Mg<sub>x</sub>Zn<sub>1–x</sub>O Alloys

Abstract

The full potential linear muffin-tin orbital (FP-LMTO) method was applied to study the structural and electronic properties of the compounds MgO, ZnO and their alloy Mg x Zn 1-x O in the zincblende and NaCl structures. Results are obtained using the local density approximation (LDA), the ground-state properties like lattice constant and bulk modulus obtained agree very well with experimental and other theoretical calculations. The effect of composition on lattice constant from Vegard's law and the bulk modulus was investigated. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. It is concluded that the energy band gap bowing is primarily due to chemical charge-transfer effect. Contribution of volume deformation and structural relaxation to the gap bowing parameter is found to be very small.

Miscibility and ordered structures of MgO-ZnO alloys under high pressure

“…At 6.5 (or 5.9 GPa for B3-ZnO considered) to 21 GPa, Mg 3 ZnO 4 is stable in the Pm -3 m structure ( L 1 2 -type, as reported in Ref. 25), and then transforms into a tetragonal I 4/ mmm structure ( D 0 22 -type), which is the same as that reported in Refs 2224…”

“…For MgZn 3 O 4 , the cubic Pm -3 m and tetragonal I 4/ mmm phases are found to be the most stable in pressure ranges of 8.5 (or 7.9 GPa for B3-ZnO considered)-68 and 68–80 GPa, respectively. The Pm -3 m MgZn 3 O 4 ( L 1 2 -type) is the same as that reported in Refs2425. MgZnO 2 is stable in the P 4/ mmm structure (same as that in Ref.…”

“…2, at 10 GPa, the energetically “deepest” structures occur at x = 0.25, x = 0.5 and x = 0.75, which have been extensively studied by many authors2223242526. Two structures were found respectively at the three compositions under pressure bellow 80 GPa, and the enthalpies difference are depicted in Fig.…”

“…In the last decade, there are numerous theoretical studies on the MgO-ZnO alloys22232425262728293031323334353637383940. Sanati et al 22 showed that isostructural MgO-ZnO alloys are stable under certain conditions using the cluster expansion (CE) method, but they also concluded that if MgO and ZnO can adopt their own crystal structures ( B 1 and B 4, respectively), the alloy is predicted to phase separate.…”

“…Very recently, combining the CASP-CE with a systematic set of first-principles total energies, Liu et al 24 exhaustively searched for the ground-state structures of MgO-ZnO alloys, and found a few structures as yet unreported. Several groups2526272829 reported their theoretical studies in which the random Mg x Zn 1−x O alloy have been simulated using special quasirandom structures (SQS) approach4142. There exist other theoretical studies303132333435, in which alloying of ZnO and MgO proceeds by substituting Mg atoms by Zn atoms in the cubic rock-salt structure or vice versa in the hexagonal wurtzite structure, and also exist several theoretical reports363738 on MgZnO 2 in various model systems.…”