Synthesis, crystal structure and physico-chemical investigations of a new lyonsite molybdate Na0.24Ti1.44(MoO4)3

Abstract New double molybdate type lyonsite, Na0.24Ti1.44(MoO4)3, has been synthesized by a solid-state reaction. Structural, vibrational, optical and electrical properties have been investigated. Its crystal structure determined from single crystal X-ray diffraction data. It crystallizes in the orthorhombic system, space group Pnma, with a ​= ​5.025(3) A, b ​= ​10.648(6) A, c ​= ​17.797(8)and Z ​= ​4. The structure can be described as a three-dimensional framework with hexagonal tunnels in which Na+ cations resides. The structural model was validated by charge distribution (CHARDI) method. X-ray powder diffraction pattern revealed the formation of a pure phase which crystallizes in the orthorhombic system. Vibrational study by means of FTIR spectroscopy confirms the existence of the (MoO4)2- functional group. Optical properties were recorded at room temperature using UV–visible spectroscopy in the spectral range 200–800 ​nm. The optical absorbance was measured to determine the optical band gap using Kubelka-Munk function. Na+ ions pathways simulation was studied by Bond Valence Site Energy (BVSE) model. Electrical analysis of our compound has been investigated using complex impedance spectroscopy (CIS) in frequency and temperature range 300 ​Hz‒4MHz and 393–573 ​K, respectively. Nyquist plots reveal the presence of two contributions, an equivalent circuit was proposed. Impedance spectroscopy studies show that the conductivity is 4.07 10−6 ​S ​cm−1 at 573 ​K and the activation energy is 0.826 ​eV.DC conductivity shows electrical conduction in the material as a thermally activated process.