Structural analysis and crystal-field calculations of Nd ³⁺ in Gd _x Lu _{1− x} TaO ₄ ( x = 0.85) polycrystalline

Abstract

The crystal structural parameters of Nd3+-doped rare earth orthotantalate GdxLu1−xTaO4 (x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction, and its emission and excitation spectra at 77 K are analysed. The relativistic model of ab initio self-consistent DV-Xα method, which is applied to the cluster NdO8 in GdxLu1−xTaO4, and the effective Hamiltonian model are used to investigate its spin—orbit and crystal-field parameters. The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm−1. According to the crystal-field calculations, 96 levels of Nd3+ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd3+:YAlO3. The results indicate that the free-ion parameters are similar to those of the Nd3+ in GdxLu1−xTaO4 and YAlO3 hosts, and the crystal-field interaction of Nd3+ in GdxLu1−xTaO4 is stronger than that in YAlO3.

Parametric Decay Instability and Dissipation of Low-frequency Alfvén Waves in Low-beta Turbulent Plasmas

“…It is clear that the threshold amplitude of PDI is low in low-beta plasmas, e.g., an Alfvén wave with amplitude as small as 10 −2 will be unstable when β < 10 −2 . The nonlinear features of PDI have been investigated by numerical simulations, including MHD and hybrid simulations, for monochromatic (Gao et al 2013b) and nonmonochromatic Alfvén waves (Malara et al 2000), at parallel and oblique propagation (Zanna 2001;Matteini et al 2010), in multiple dimensions (Matteini et al 2010;Gao et al 2013a), with multiple ion species (Gao et al 2013b), and in expanding solar wind (Tenerani & Velli 2013;Del Zanna et al 2015). These studies focused on PDI in quiescent plasmas.…”