Lattice dynamics of orthorhombic NdGaO3

Abstract

A complete set of infrared-active and Raman-active lattice modes is obtained from density functional theory calculations for single-crystalline centrosymmetric orthorhombic neodymium gallate. The results for infraredactive modes are compared with an analysis of the anisotropic long-wavelength properties using generalized spectroscopic ellipsometry. The frequency-dependent dielectric function tensor and dielectric loss function tensor of orthorhombic neodymium gallium oxide are reported in the spectral range of 80-1200 cm −1. A combined eigendielectric displacement vector summation and dielectric displacement loss vector summation approach augmented by considerations of lattice anharmonicity is utilized to describe the experimentally determined tensor elements. All infrared-active transverse and longitudinal optical mode pairs obtained from density functional theory calculations are identified by our generalized spectroscopic ellipsometry investigation. The results for Raman-active modes are compared to previously published experimental observations. Static and high-frequency dielectric constants from theory as well as experiment are presented and discussed in comparison with values reported previously in the literature.

Infrared active phonons in monoclinic lutetium oxyorthosilicate

“…For comparison, (c) shows the ellipsometry investigation reported previously in Ref. 62 for Y2SiO5. We note overall excellent agreement between theory and experiment.…”

“…The usefulness of the inclusion of these forms during the analysis of phonon modes from ellipsometry data has been recently demonstrated for monoclinic β-Ga 2 O 3 , 37 CdWO 4 , 61 YSO, 47 and orthorhombic NdGaO 3 . 62 With ω → 0, Eq. 6 provides the Schubert-Lyddane-Sachs-Teller (S-LST) relationship for crystals with arbitrary symmetry, which relates the DC and high-frequency tensors with all TO and LO modes within a given crystal 60,70 det{ε…”

“…Note that all spectra for ε, ε −1 , det{ε}, and det{ε −1 } are evaluated simultaneously to achieve best-match and to find the best-match calculated model parameters. 47,61,62…”

“…3. TO-LO ruleAs pointed out by Mock et al,62 the Schubert-BUL form (Eq. 7) can be used to identify violations of the TO-LO order.…”

Anisotropic dielectric functions, band-to-band transitions, and critical points in α-Ga2O3

“…where b denotes the anharmonic broadening parameter. 38,39 We note that excitonic contributions to the M 0 -CP are interpreted as due to ground state contributions from threedimensional effective hydrogen atom-like excitons, while excitonic contributions to the M 1 -CP are interpreted as twodimensional effective hydrogen atom-like (a.k.a. hyperbolic) excitons.…”