Adisak Boonchun

Identification of Mn site in Pb(Zr,Ti)O3 by synchrotron x-ray absorption near-edge structure: Theory and experiment

Synchrotron x-ray absorption near-edge structure (XANES) experiments are performed on Mn-doped PbZr1−xTixO3 samples (PZT) and compared with first-principles XANES simulations. The features of the measured Mn K-edge XANES are consistent with the first-principles XANES of Mn on the Ti∕Zr site and inconsistent with Mn on other sites. The clear agreement between measured and first-principles theoretical XANES spectra reported here is by far the strongest evidence of Mn substituting for Ti∕Zr in PZT. This work illustrates that a first-principles supercell framework, which is popularly used to study impurities in crystals, can be used in conjunction with XANES measurement in order to identify an impurity structure with a high degree of confidence. This approach may thus be broadly applicable to study impurities in other crystals.

First principles study of Mn impurities in PbTiO3 and PbZrO3

A first principles study of an Mn impurity in PbTiO3 and PbZrO3 has been carried out to determine its favorable location and its electronic and magnetic properties. We find that it is energetically favorable for the Mn atom to substitute for Ti∕Zr (as opposed to substituting for Pb and O or to residing in an interstitial position) under all equilibrium crystal growth conditions. The Mn defect mainly occurs as neutral-charge Mn substitute Ti∕Zr, which has a total electron spin of 3∕2. When no other impurities are present, a small concentration of charged Mn impurities that also form tends to make the sample slightly p type (n type) in oxygen-rich (poor) equilibrium growth conditions.

Electronic structure, doping, and lattice dynamics of LiGaO2

First-principles calculations are used to study the properties of LiGaO2, a potentially useful opto-electronic material in conjunction with ZnO. Its band structure is evaluated using the quasiparticle self-consistent GW method. The band gap is found to be significantly larger than the reported room temperature absorption onset. Estimates are made of the finite temperature and excitonic corrections. Potential n- and p-type dopants are studied in the local density approximation, using a supercell approach. The lattice dynamical properties are studied using the density functional perturbation method.

Bond lengths, phase stability, and band gaps in MgxZn1−xO alloys

The main question studied in this article is how the preference of MgO for six- or fivefold bonding in rocksalt or h-MgO structures, respectively, affects the local bond lengths near Mg atoms in wurtzite structured MgxZn1−xO alloys. A first-principles study of MgxZn1−xO alloys has been carried out in the range 0<x<0.5 to determine the local wurtzite parameter u, axial bond lengths, and the band gaps. Disorder in the alloys is simulated using the special quasirandom structure approach. The authors found that axial Mg–O bond lengths are longer than the axial Zn–O bond lengths for all possible concentrations, but the u values are still far away from the h-MgO value of 0.5. The band gap is found to increase linearly with Mg content. They found no signs of transformation to the lower energy h-MgO structure until x is about 50%.