Na/Li substitution effect on the structural, electrical and magnetic properties of LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2

Abstract

The novel bi-molybdate β─Li0.87Na0.13Cr(MoO4)2 was prepared by solid state reaction route. Single crystal X-ray diffraction experiment revealed that the compound crystallizes in the triclinic system, in P −1 space group with a = 6.715 (2), b = 7.160 (3), c = 7.237 (1) Å, α = 91.16° (3), β = 110.59° (2), γ = 105.54° (3). Its crystal structure is isotypic to LiCr(MoO4)2 which has interesting magnetic and electrochemical properties [1–3]. Bond valence sum (BVS) and charge distribution (CHARDI) validation tools supported the structural model.The electrical properties were systematically studied by impedance spectroscopy. The ionic conductivity measurements are performed on pellets of 82% and 87% relative density for LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2 respectively. AC impedance spectroscopy studies show that the highest overall conductivity is σ326°C = 7.86 × 10−7 S cm−1Probable diffusion pathways of Li+ ions in the both structures were simulated using the bond valence sum BVS maps method. This analysis shows that the ionic transport in these materials is essentially due to simple hopping of Li+ ions parallel to (101) plane.For β─Li0.87Na0.13Cr(MoO4)2 compound, the in-situ High Temperature X-Ray Diffraction (HTXRD), in the temperature range from 25 to 650 °C, were also performed and Unit-cell thermal expansion has been discussed.The magnetic study show that these compounds present an antiferromagnetic order below the temperatures TN = 16 and 30 K for LiCr(MoO4)2 and β─Li0.87Na0.13Cr(MoO4)2 respectively.