Effect of the processing parameters on the crystalline structure of lanthanide orthotantalates

Abstract

The influence of the synthesis parameters on the crystalline structures of orthotantalate 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 LnTaO 4 compounds besides the lanthanide ionic size. Firstly, the thermal evolution for NdTaO 4 samples showed that mixed crystal phases are formed up to 1100 °C, while well-crystallized M-NdTaO 4 (I2/a) materials are obtained in temperatures higher than 1200 °C. Also, the influence of the synthesis time was investigated for the LaTaO 4 ceramics: it was necessary 14 h to obtain samples in the P2 1 /c structure. Finally, two polymorphs could be obtained for the DyTaO 4 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 orthotantalate materials.

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO4

“…Data at either side of this transition could be fitted reasonably well to the same C mc 2 1 model, hence dismissing the assumption that this was a transition to the paraelectric C mcm phase. It is also noted that investigations by Vullum, et al, [ 15 ] and Cava and Roth [ 16 ] show LaTaO 4 maintains the C mc 2 1 space group up to at least 570 K.…”

Structural phase transitions in the geometric ferroelectric LaTaO4

“…LaTaO 4 is the only n = 2 ferroelectric oxide reported to date and its basic structural properties have been well established [8][9][10][11][12]. Mode analysis of the Cmc2 1 phase shows the presence of two gamma modes, 1 + and 2 − , with reference to the parent Cmcm structure.…”

X‐ray photoelectron spectroscopy study of neodymium niobate and tantalate precursors and thin films

“…Neodymium niobate NdNbO 4 (NNO) and tantalate NdTaO 4 (NTO) ceramics and films possess mixed types of conduction processes, including protonic, ionic, and electronic conduction which is determined by fabrication conditions, and these materials are promising for sensors, solid fuel cell electrolytes, and high-temperature proton conductors. [1][2][3][4][5] One of the most detailed structural studies on LnMO 4 (Ln = rare earths; M = Nd, Ta), which covers lanthanide ions, were implemented by Siqueira et al [6][7][8][9] For these materials, several polymorph modifications are known. At room temperature, these compounds crystallize in the monoclinic M-and M′-fergusonite structures and transformed to the tetragonal T scheelite-type structure 3 depending on sol-gel synthesis conditions.…”