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Several nanocrystalline SbO2phase materials were produced by annealing the as-synthesized Sb2O3phase materials obtained by varying (0 to 2500 ml) the quantity of deionized water as a solvent in the precipitation process at 700 °C/3 h. The existing high-pressure and high-temperature (HPHT) method yielded the monoclinic β-Sb2O4phase (C12/c1) for the α-Sb2O4powder (obtained by heating the Sb2O3powder in an oxygen atmosphere at 530 °C/24 h), whereas the present conventional heat treatment on the as-prepared Sb2O3phase materials shows the formation of an orthorhombic SbO2phase. All the annealed materials crystallized in orthorhombic structure with space group, Pna21(33)without any impurity despite the as-obtained Sb2O3phase materials varied in purity and symmetry. The formed SbO2phase materials showed no significant change in the orthorhombic lattice parameters, despite a comparable variation in the average crystalline size. The thermal, Raman, and micro-structural features of these nanocrystalline SbO2phase materials are further characterized by TG/DTA, Raman spectrometer, and FESEM-EDX techniques, respectively. Different morphological features of bar-shaped, spherical, and agglomerated particles are observed in the formed SbO2phase materials.

BaMoO4is a special type of material that is suitable for photocatalysts, scintillating medium, solid-state laser, and optical fibers applications. The effect of different methods using different precursors by ball milling and co-precipitation and their characterizations details of different BaMoO4materials are reported here. Regardless of the employed methods, all the samples are crystallized in tetragonal symmetry with space group, I41/a(88) in phase pure form. The ball-milled BaMoO4materials show relatively broad reflections with reduced crystalline size (~ 20 nm) than the co-precipitation methods (~ 70 nm). Agglomerated nature of round-shaped particles is seen for the ball-milled BaMoO4materials which differ from the morphology of the co-precipitation processed materials having different shapes and sizes in the range of ~ 227–453 nm. UV–Vis absorption results reveal the optical band gap of 3.51–4.35 eV for the different BaMoO4materials. The Raman analysis features well support the optical properties of the BaMoO4phase. Among the different as-prepared materials, the NIR reflectance spectrum of BaMoO4materials obtained via the co-precipitation method exhibits relatively higher reflectance in the entire NIR region. The presently investigated BaMoO4materials (co-precipitation) show better NIR reflectance than the other type of scheelite (BiVO4and SrMoO4) materials.

A simple room-temperature synthesis procedure is reported here to obtain pure cubic Sb2O3phase from the precursors, KSbO.C4H4O6and KOH. The quality, thermal, microstructural, and optical properties of as obtained materials are reported. The XRD pattern confirms the presence of polycrystalline cubic Sb2O3phase with a lattice parameter, a= 1.1161(3) nm. The precursor, KSbO.C4H4O6calcined at 350–900 °C yielded different products, unlike the single-step precipitation method. The morphology of octahedron-shaped grains to the size of 1.46–1.59 µm is observed for the as obtained Sb2O3phase. The exothermic peak temperature (633 °C) of the as obtained present Sb2O3phase materials with low weight loss of ~ 3.5% is slightly higher indicating the microcrystallinity of the materials. The analyzed different spectroscopic results validate the characteristics of the cubic Sb2O3phase.

The nanocrystalline AWO4(A = Ba, Sr, and Ca) materials were obtained by combustion followed by annealing at 800 °C for 3 h by using the nitrate salts of A = Ba, Sr, and Ca and other required raw materials. The XRD, TG–DTA, FT-IR, Raman, UV–Vis, FESEM, and EDX results of the AWO4series are presented in this article. The as-prepared combustion products show mixed phases, whereas the annealed samples yield pure scheelite phase, AWO4, crystallized in a tetragonal, I41/a (88) structure. The refined lattice parameters of the scheelite phases significantly vary with the difference in the ionic radii of the alkaline earth metals (A). The band gap (Eg) values obtained from Tauc plots are found as 5.63, 5.3, and 5.12 eV for A = Ba, Sr, and Ca, respectively, in the AWO4series.

The Zn1-xBixO (0 ≤ x≤ 0.1) combustion products were synthesized by solution combustion method using Zn(NO3)2·6H2O and Bi(NO3)3·5H2O as oxidizers and glycine as a fuel. To enhance the solubility of Bi in the ZnO hexagonal structure, the different portions of the combustion products were subsequently annealed (600 °C/5 h) and ball-milled under 350 rpm for 10 h. The various multifunctional Zn1-xBixO materials were analyzed by different characterization techniques (XRD, TG–DTA, FT-IR, NIR, Raman, and FESEM-EDX) to explore the physico-chemical properties. In a wide range of composition (x), only the x= 0 and 0.02 revealed a single hexagonal phase with a Zn1-xBixO structure for the combustion products and annealed samples. Remarkably, the multifunctional nanocrystalline Zn1-xBixO (0 ≤ x≤ 0.1) materials were successfully obtained in phase pure form upon subsequent ball-milling of the combustion products, while the annealing treatment failed to enhance the solubility of Bi for x= 0.04, 0.06, 0.08, and 0.1. As the combustion products and annealed materials show higher NIR reflectance in the NIR region for x= 0, 0.02, maybe used as solar protecting color pigment materials. Though the ball milling of combustion products enhanced the solubility of Bi in the ZnO structure, it heavily affected the NIR reflectance of Zn1-xBixO. Agglomeration of fine particles is observed in the FESEM micro-images of Zn1-xBixO; x= 0.1 (ball-milled) materials. From the present research findings, we conclude that high-energy ball milling has a substantial impact on the phase formation and the properties of the ball-milled Zn1-xBixO samples.