Simulation of Simple and Complex Gadolinium Molybdates by the Interatomic Potential Method
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TAL CHEMISTRY
First Russian Crystallographic Congress
Simulation of Simple and Complex Gadolinium Molybdates by the Interatomic Potential Method V. B. Dudnikovaa,* and E. V. Zharikovb a Lomonosov
b
Moscow State University, Moscow, 119991 Russia Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia *е-mail: [email protected] Received June 2, 2017
Abstract—Crystals of ferroelectric‒ferroelastic gadolinium molybdate Gd2(MoO4)3, calcium molybdate CaMoO4, and double sodium‒gadolinium molybdates of stoichiometric (Na1/2Gd1/2MoO4) and cationdeficient (Na2/7Gd4/7MoO4) compositions, which are used to design solid-state lasers, phosphors, and white LEDs, have been simulated by the interatomic potential method. Their structural, mechanical, and thermodynamic properties are calculated using a unified system of interatomic potentials and effective ion charges, which demonstrated transferability and made it possible not only to describe the existing experimental data but also to predict some important physical and thermodynamic properties of molybdate crystals. The influence of the deviation from stoichiometry and partial ordering of cations on sites in nonstoichiometric crystals on the properties and local structure of sodium‒gadolinium molybdates is discussed. DOI: 10.1134/S1063774518020050
INTRODUCTION Simple and complex molybdates are of great interest as materials for solid-state lasers, phosphors, and white LEDs [1, 2]. Atomistic simulation allows one to characterize rapidly and adequately these systems and investigate their structural, mechanical, and thermodynamic properties. The object of our study, gadolinium molybdate Gd2(MoO4)3 of orthorhombic modification (β'-GMO), exhibits ferroelectric and ferroelastic properties; it is also a promising material for solid-state lasers. Another intensively studied simple molybdate is calcium molybdate CaMoO4. It demonstrates efficient Raman scattering and nonlinear optical properties, which are used in practice. Double molybdates and tungstates of alkaline and rare-earth elements and their solid solutions belong to a large family of compounds described by the general formula MmRenTO4 (where M = Li, Na, K; Re = Y, La, Gd, Lu …; T = Mo, W) and crystallizing into several different structure types [3, 4]. They can exist in the form of either stoichiometric (m = n = 1/2) or cationdeficient (m < n) compounds of significantly different compositions [5, 6], some of which (according to the data of [7]) have an incommensurately modulated structure. Among double molybdates and tungstates, crystals with scheelite structure and scheelite-like
compounds are of particular interest in view of their good spectral-luminescence characteristics and the technological efficiency of devices based on them. In this paper, we report the results of simulating crystals of gadolinium-containing molybdates by the interatomic potential method, including the development (by an example of simple molybdates) of a unified system of interatomic potentials that can also be u
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