Utilizing a unified structure model in (3+1)-dimensional superspace to identify a homologous phase (Ga1-alpha Al alpha)(2)O-3(ZnO)(m) in ZnO-based thermoelectric composites

A unified structure model in (3+1)-dimensional superspace proved suitable for identification of a homologous phase (Ga1-alpha Al alpha)(2)O-3(ZnO)(m) by the profile fitting of powder X-ray diffraction intensities for thermoelectric composite materials in the pseudoternary system ZnO-Al2O3-Ga2O3. A homologous compound of the phase parameter m similar or equal to 37 was found to coexist with (Al,Ga)-doped ZnO in samples sintered at 1723K in air. The thermoelectric properties of the composite materials were closely related to the phase fractions. The higher the phase fraction of (Al,Ga)-doped ZnO with the wurtzite structure, the higher the electrical conductivity. On the other hand, the homologous compound with the long-period structure was effective in lowering the thermal conductivity of the materials.