Effect of the processing parameters on the crystalline structure of lanthanide ortho tantalates

The influence of the synthesis parameters on the crystalline structures of ortho tantalate ceramics has been investigated. Powder materials were prepared by the solid-state reaction route. X-ray diffraction and Raman scattering measurements were employed to investigate the crystal structure of the produced materials. In this work, we analyzed three different examples in which the temperature and time were decisive on the final crystal structure of LnTaO4 compounds besides the lanthanide ionic size. Firstly, the thermal evolution for NdTaO4 samples showed that mixed crystal phases are formed up to 1100 °C, while well-crystallized M-NdTaO4 (I2/a) materials are obtained in temperatures higher than 1200 °C. Also, the influence of the synthesis time was investigated for the LaTaO4 ceramics: it was necessary 14 h to obtain samples in the P21/c structure. Finally, two polymorphs could be obtained for the DyTaO4 ceramics: P2/a and I2/a space groups were obtained at 1300 °C and 1500 °C, respectively. This study indicated that the temperature, time and lanthanide size are directly correlated with the crystalline arrangement of the ortho tantalate materials.(author)