Properties of the new electronic device material LaGdO3

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Abstract

The room temperature crystal structure of potential high-k dielectric LaGdO3 has been analyzed by X-ray diffraction techniques and its structural evolution with temperature has been probed by Raman spectroscopy. Rietveld refinement of the ambient XRD data established the perfectly layered B-type monoclinic crystal structure with a = 14.43 Å, b = 3.68 Å, c = 8.99 Å, and β = 100.57° which is further validated by the 21 (14 Ag and 7 Bg) Raman-active vibrational modes with centro-symmetric space group math formula or C2/m. Atomic positions, coordination numbers, inter-ionic lengths, etc. were derived using Rietveld analysis. All prominent Bragg peaks were successfully indexed. Temperature dependent Raman spectra of LaGdO3 from 80 to 1400 K were analyzed using the damped harmonic oscillator model. The softening and hardening of vibrational modes are reported. Above 900 K, disappearance of all high frequency modes (>600 cm−1) and merger of several mid frequency modes (between 200 and 500 cm−1) into two distinct modes was observed, a direct evidence of a possible structural phase transition from monoclinic to tetragonal/pseudocubic.

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