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The single crystals of Na 2 Mn 2 (MoO 4) 3 were successfully grown using the solid-state synthesis method. This compound crystallizes in a triclinic system with space group P 1 ‾ (C i). Its structure can be described as a three-dimensional anionic framework of Mn 2 O 10 double octahedra units sharing edges with the MoO 4 tetrahedra. The Na+ ions are disordered and located in the voids forming infinite channels running along the [100], [010] and [001] directions. The structural model was validated by the bond valence sum (BVS) and charge distribution (CHARDI) methods. The polycrystalline powder of Na 2 Mn 2 (MoO 4) 3 was prepared as well using citrate process. The obtained sample was characterized by powder X-ray diffraction, infrared spectroscopy and Raman scattering at room temperature. The vibrational study confirms the existence of the MoO 4 2− functional groups. Thermal stability of the studied material was analyzed using differential scanning calorimetry. The Na 2 Mn 2 (MoO 4) 3 compound is thermally stable up to 500 °C. Magnetic susceptibility measurements reveal that the title compound is antiferromagnetic with Néel temperature T N = 6.5 (5) K. At higher temperatures, its susceptibility follows a Curie–Weiss law. Electrical measurements of this material were studied by means of the impedance spectroscopy technique, in 0.1 Hz–4 MHz frequency and in 443–691 K temperature ranges. The conductivity of Na 2 Mn 2 (MoO 4) 3 is 2.30 μScm−1 at 691 K and it is thermally activated with energy of 0.47 eV. The sodium migration pathways in the crystal structure were investigated using the bond valence sum pathways (BVSP) analysis and the bond valence site energy (BVSE) model. Image 1 • A new single crystal of Na 2 Mn 2 (MoO 4) 3 was grown by solid state reaction. • The structure was determined by single-crystal X-ray diffraction. • Magnetic susceptibility measurements revel that Na 2 Mn 2 (MoO 4) 3 is antiferromagnetic. • Na+ ionic conductivity was studied by complex impedance spectroscopy. [ABSTRACT FROM AUTHOR]

In this paper, Na 2 Mn 2 (MoO 4) 3 doubgyle molybdate was prepared by sol-gel method to investigate the structural, morphological and optical properties. X-ray diffraction analysis showed that Na 2 Mn 2 (MoO 4) 3 crystallizes in the triclinic system in the P 1 ¯ group. The composition and morphology of the compound were checked by energy dispersive spectroscopy coupled with scanning electron microscope. Optical properties were analyzed by UV–Vis diffuse reflectance spectroscopy. The photocatalytic properties were evaluated by the degradation of methylene blue under natural sunlight and compared to Xe and UV lamps. The highest photodegradation efficiency (85.3%) was obtained for solar irradiation, therefore, Na 2 Mn 2 (MoO 4) 3 can be a potential photocatalyst for the removal of dye wastewater pollution driven by visible-light. The proposed mechanism of photodegradation in water involves creation of hydroxyl radicals and superoxide anions that attack the methylene blue molecules and decompose it to carbon dioxide and water. Fig. Scheme of electron excitation/recombination process during, irradiation with sunlight of Na 2 Mn 2 (MoO 4) 3 compound in solution of MB dye, band structures and mineralization of methylene blue (MB) dye molecules. [Display omitted] • A visible light driven photocatalysis Na 2 Mn 2 (MoO 4) 3 was prepared by sol-gel method. • Reflectance measurements were used to calculate the refractive index, the absorption index and the optical parameters. • The photocatalytic properties of Na 2 Mn 2 (MoO 4) 3 ​powder were evaluated by the degradation of methylene blue under natural sunlight and compared to Xe and UV lamps. [ABSTRACT FROM AUTHOR]

New double molybdate type lyonsite, Na 0.24 Ti 1.44 (MoO 4) 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 P nma, with a ​= ​5.025(3) Å, b ​= ​10.648(6) Å, 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 (MoO 4)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. [Display omitted] • A new single crystal of Na 0.24 Ti 1.44 (MoO 4) 3 was grown by solid state reaction. • The structure was determined by single-crystal X-ray diffraction. • The conduction pathways for Na ​+ ​cations are simulated using the BVSE model. • Na ​+ ​ionic conductivity was studied by complex impedance spectroscopy. [ABSTRACT FROM AUTHOR]