No abstract

The concentration of native point defects in CuInSe2 powder material as a function of stoichiometry has been experimentally determined by neutron powder diffraction. A correlation between the Cu/In ratio and the density of VCu as well as InCu has been established and their concentrations are quantified. It is demonstrated, that assuming the spontaneous formation of defect pairs, the density of native point defects is reduced significantly by an order of magnitude. The functionality of a solar device, assuming same conditions like in the analyzed material, may be explained by a neutralization due to the formation of electrically inactive defect complexes.

The LaCo1−xFexO3 compounds have been investigated by means of neutron powder diffraction (NPD), x-ray powder diffraction (XPD) and magnetization measurements. The NPD and XPD patterns were successfully refined as rhombohedral (x≤0.5) and orthorhombic (x≥0.6). The temperature-induced transition from the rhombohedral phase into the orthorhombic one is characterized by a two-phase crystal structure state. Magnetization and neutron powder measurements have revealed that compounds with x<0.4 exhibit a paramagnetic-like behaviour, whereas for x≥0.4 samples a weak ferromagnetic component was observed. The NPD patterns were successfully refined by admitting a Gz spatial orientation of the antiferromagnetic vector. The magnetic properties of the LaCo1−xFexO3 samples can be explained assuming a low spin state of the Co3+ ions, whereas antiferromagnetism is caused by magnetic interactions between the Fe3+ ions. Based on the obtained data the combined crystal and magnetic phase diagram has been constructed.

Competing Jahn-Teller distortions combined with geometrical frustration give rise to a rich phase diagram as a function of x(Cu) and temperature in the spinel system Ni1xCuxCr2O4. The Jahn-Teller distortion of the end members acts in opposite ways with an elongation of the NiO4 tetrahedra resulting in a structural transition at TS1 = 317 K in NiCr2O4, but a flattening in the CuO4 tetrahedra at TS1 = 846 K in CuCr2O4, in both cases the symmetry is lowered from cubic (