Synthesis, Structural, Thermal, and Electronic Properties of Palmierite-Related Double Molybdate α-Cs2Pb(MoO4)2

Photocatalytic activity and magnetic properties of Ba2FeMoO6 ferromagnetic double perovskite

Ba2FeMoO6 samples were prepared using the sol-gel method without and using Cetyltrimethylammonium bromide (CTAB) to study their photocatalytic properties. The structural and morphological properties of the samples were characterized systematically. The Rietveld refinement described a cubic structure with space group Fm-3m and a single phase with no detectable impurity for either. FESEM images showed that the sample's morphology changed significantly with the addition of the CTAB. The BET analysis of the sample containing CTAB (BFMOC) showed that the special surface area of the pores increased ten times compared to parent sample and its pore size decreased. The UV-Vis spectrum of the BFMOC sample showed two absorption peaks at 223 nm and 705 nm in the ultraviolet and visible regions, respectively. Diffuse reflectance spectroscopy (DRS) spectra of the samples showed direct band gaps (∼2eV) for both. Photocatalytic and absorbent properties were observed in both samples. The photocatalytic properties of the samples revealed that they effectively degraded the dye triphenylmethane MG. By adding CTAB, the Curie temperature of the BFMO sample increased from 304 K to 310 K, while saturation magnetization decreased from ∼1.43 μB/f.u to ∼0.89 μB/f.u. The low coercive field value indicates that the both samples possess soft magnetic and ferromagnetic properties.

Structural Studies and Thermal Analysis in the Cs2MoO4-PbMoO4 System with Elucidation of β-Cs2Pb(MoO4)2

The quaternary compound Cs₂Pb(MoO₄)₂ was synthesized and its structure was characterized using X-ray and neutron diffraction from 298 to 773 K, while thermal expansion was studied from 298 to 723 K. The crystal structure of the high-temperature phase β-Cs₂Pb(MoO₄)₂ was elucidated, and it was found to crystallize in the space group R3̅m (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase α-Cs₂Pb(MoO₄)₂ was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs₂MoO₄-PbMoO₄ system were performed, revisiting a previously reported phase diagram. The equilibrium phase diagram proposed here includes a different composition of the intermediate compound in this system. The obtained data can serve as relevant information for thermodynamic modeling in view of the safety assessment of next-generation lead-cooled fast reactors.

Structural, Spectroscopic, Electric and Magnetic Properties of New Trigonal K5FeHf(MoO4)6 Orthomolybdate

A new multicationic structurally disordered K₅FeHf(MoO₄)₆ crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K₅FeHf(MoO₄)₆ was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO₄ tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm^-1 is in a good agreement with the simulated phonon density of the states. K₅FeHf(MoO₄)₆ is a paramagnetic down to 4.2 K. The negative Curie-Weiss temperature of -6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K₅FeHf(MoO₄)₆ are 2.97 and 3.21 eV, respectively. The K₅FeHf(MoO₄)₆ bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe³⁺ ions.

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1-xCaGd0.5Ho0.05Yb0.45(MoO4)3 Scheelite-Type Upconversion Phosphors

A set of new triple molybdates, Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45, was successfully manufactured by the microwave-accompanied sol–gel-based process (MAS). Yellow molybdate phosphors Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45 with variation of the Li_xNa_1-x (x = 0, 0.05, 0.1, 0.2, 0.3) ratio under constant doping amounts of Ho³⁺ = 0.05 and Yb³⁺ = 0.45 were obtained, and the effect of Li⁺ on their spectroscopic features was investigated. The crystal structures of Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) at room temperature were determined in space group I4₁/a by Rietveld analysis. Pure NaCaGd_0.5Ho_0.05Yb_0.45(MoO₄)₃ has a scheelite-type structure with cell parameters a = 5.2077 (2) and c = 11.3657 (5) Å, V = 308.24 (3) ų, Z = 4. In Li-doped samples, big cation sites are occupied by a mixture of (Li,Na,Gd,Ho,Yb) ions, and this provides a linear cell volume decrease with increasing Li doping level. The evaluated upconversion (UC) behavior and Raman spectroscopic results of the phosphors are discussed in detail. Under excitation at 980 nm, the phosphors provide yellow color emission based on the ⁵S₂/⁵F₄ → ⁵I₈ green emission and the ⁵F₅ → ⁵I₈ red emission. The incorporated Li⁺ ions gave rise to local symmetry distortion (LSD) around the cations in the substituted crystalline structure by the Ho³⁺ and Yb³⁺ ions, and they further affected the UC transition probabilities in triple molybdates Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45. The complex UC intensity dependence on the Li content is explained by the specificity of unit cell distortion in a disordered large ion system within the scheelite crystal structure. The Raman spectra of Li_xNa_1-xCaGd_0.5(MoO₄)₃ doped with Ho³⁺ and Yb³⁺ ions were totally superimposed with the luminescence signal of Ho³⁺ ions in the range of Mo–O stretching vibrations, and increasing the Li⁺ content resulted in a change in the Ho³⁺ multiplet intensity. The individual chromaticity points (ICP) for the LiNaCaGd(MoO₄)₃:Ho³⁺,Yb³⁺ phosphors correspond to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

Exploration of the Structural and Vibrational Properties of the Ternary Molybdate Tl5BiHf(MoO4)6 with Isolated MoO4 Units and Tl+ Conductivity

The phase relations in the subsolidus region of the Tl₂MoO₄-Bi₂(MoO₄)₃-Hf(MoO₄)₂ system were studied with the "intersecting cuts" method. The formation of the novel ternary molybdate Tl₅BiHf(MoO₄)₆ is found in this ternary system. The compound has a phase transition at T_pt = 731 K (ΔH = -3.15 J/g) and melts at T_m = 871 K (ΔH = -41.71 J/g), as determined by a thermal analysis. Tl₅BiHf(MoO₄)₆ single crystals were obtained by the spontaneous nucleation method. The crystal structure of Tl₅BiHf(MoO₄)₆ was revealed by structure analysis methods. This molybdate crystallizes in the trigonal space group R3̅c with the unit cell parameters a = 10.6801(4) Å, c = 38.5518(14) Å, V = 3808.3(2) ų, and Z = 6. The vibrational characteristics of Tl₅BiHf(MoO₄)₆ were determined by Raman spectroscopy. The Tl₅BiHf(MoO₄)₆ conductivity was measured at frequencies of 0.1, 1.0, and 10 kHz in the temperature range of 293-773 K; in this temperature range, the conductivity level was 10^-12-10^-7 S/cm.

MOF-Confined Sub-2 nm Stable CsPbX3 Perovskite Quantum Dots

The metal halide with a perovskite structure has attracted significant attention due to its defect-tolerant photophysics and optoelectronic features. In particular, the all-inorganic metal halide perovskite quantum dots have potential for development in future applications. Sub-2 nm CsPbX₃ (X = Cl, Br, and I) perovskite quantum dots were successfully fabricated by a MOF-confined strategy with a facile and simple route. The highly uniform microporous structure of MOF effectively restricted the CsPbX₃ quantum dots aggregation in a synthetic process and endowed the obtained sub-2 nm CsPbX₃ quantum dots with well-dispersed and excellent stability in ambient air without a capping agent. The photoluminescence emission spectra and lifetimes were not decayed after 60 days. The CsPbX₃ quantum dots maintained size distribution stability in the air without any treatment. Because of the quantum confinement effect of CsPbX₃ quantum dots, the absorption and photoluminescence (PL) emission peak were blue shifted to shorter wavelengths compare with bulk materials. Furthermore, this synthetic strategy provides a novel method in fabricating ultra-small photoluminescence quantum dots.

Effect of Thermochemical Synthetic Conditions on the Structure and Dielectric Properties of Ga1.9Fe0.1O3 Compounds

We report on the tunable and controlled dielectric properties of iron (Fe)-doped gallium oxide (Ga₂O₃; Ga_1.9Fe_0.1O₃, referred to as GFO) inorganic compounds. The GFO materials were synthesized using a standard high-temperature, solid-state chemical reaction method by varying the thermochemical processing conditions, namely, different calcination and sintering environments. Structural characterization by X-ray diffraction revealed that GFO compounds crystallize in the β-Ga₂O₃ phase. The Fe doping has induced slight lattice strain in GFO, which is evident in structural analysis. The effect of the sintering temperature (T_sint), which was varied in the range of 900-1200 °C, is significant, as revealed by electron microscopy analysis. T_sint influences the grain size and microstructure evolution, which, in turn, influences the dielectric and electrical properties of GFO compounds. The energy-dispersive X-ray spectrometry and mapping data demonstrate the uniform distribution of the elemental composition over the microstructure. The temperature- and frequency-dependent dielectric measurements indicate the characteristic features that are specifically due to Fe doping in Ga₂O₃. The spreading factor and relaxation time, calculated using Cole-Cole plots, are in the ranges of 0.65-0.76 and 10^-4 s, respectively. The results demonstrate that densification and control over the microstructure and properties of GFO can be achieved by optimizing T_sint.

Syntheses, crystal structures and photoluminescence properties of two rare-earth molybdates CsLn(MoO4)2 (Ln=Eu, Tb)

Single crystals of two cesium rare-earth molybdates CsLn(MoO4)2 (Ln=Eu, Tb) have been prepared using the high temperature molten salt (flux) method. Single-crystal X-ray diffraction analyses reveal that they crystallize in the orthorhombic space group Pccm (No. 49) and features a 2D layer structure that is composed of [Ln(MoO4)2]∞ and [Cs]∞ layers. Under near-UV light excitation, emission spectrum of CsEu(MoO4)2 consists of several sharp lines due to the characteristic electronic transitions of Eu3+ ions, whereas CsTb(MoO4)2 exhibits characteristic green emission of Tb3+ ions.