Intra-grain polarized infrared spectroscopy realized in domain-engineered Zn2GeO4 ceramics

Intra-grain infrared spectroscopy was carried out on a domain-engineered ceramic with abnormally large grains. The model system used was a polycrystalline Zn₂GeO₄ ceramic sample, with a rhombohedral $R\overline{3}$ crystal structure and giant grain microstructure (50–350 μm). The micro-infrared spectra unveiled preferential crystal orientations for the different grains. Polarized spectra revealed well-defined crystallographic domains inside the ceramic grains. Appropriate crystallographic planes for full assignment of the infrared modes were found by polarized infrared light. This allowed the first realization of a polarization-resolved symmetry assignment of an as-grown ceramic material. A sound description of the polar phonon features of rhombohedral Zn₂GeO₄ is then presented. Also, an infrared spectroscopic mapping of the crystallographic domains inside the ceramic grains is demonstrated.