MS16-P12 Dielectric, pyroelectric and structural properties of rare-earth calcium oxoborates RCa4Although rare-earth oxoborates are known since 1991 , they have been studied mainly for their non-linear optical properties that are useful for Laser applications. Recently, these materials gathered interest due to their piezoelectric properties, which are not only stable up to high temperatures , but also unimpaired by phase transitions. Furthermore, the materials lend themselves to rare-earth substitution, thus, offering a systematic possibility to tweak their properties. However, the low symmetry of their monoclinic structure of space group Cm complicates characterisation. Here, we report on the dielectric and pyroelectric properties of some rare-earth calcium oxoborates and present high-temperature powder diffraction data giving insight into possible structural instabilities around temperatures of 1000 K.
Samples of rare-earth calcium oxoborates RCa2Ca2O(BO3)3 with R = Gd, Y, Er, La were cut and polished from large Czochralski-grown single-crystals. The four components of the dielectric tensor were investigated at room temperature with the substitution method. Furthermore, the two components of the pyroelectric tensor were measured via the Sharp-Garn method from room temperature to 420 K. The stability of noble metal electrodes was investigated up to 1200 K.
High-temperature X-ray powder diffraction patterns obtained on samples milled from crystals exhibit a discontinuity in the expansion of the crystal lattice at elevated temperatures for R = Gd, La, Y, Sm. Comparing the initial and final diffraction patterns reveals changes in the cation ordering due to the thermal treatment.References:
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 Yu, F., Hou, S., Zhao, X., Zhang, S, IEEE Trans. Ultrason., Ferroelect., Freq. Control, 61, 1344–1356 (2014)Keywords: borate dielectric pyroelectric