Crystalline hydrate of double cesium europium sulfate [CsEu(H₂O)₃(SO₄)₂]·H₂O was synthesized by the crystallization from an aqueous solution containing equimolar amounts of 1Cs⁺:1Eu³⁺:2SO₄²⁻ ions. Anhydrous salt CsEu(SO₄)₂ was formed as a result of the thermal dehydration of the crystallohydrate. The unusual effects observed during the thermal dehydration were attributed to the specific coordination of water molecules in the [CsEu(H₂O)₃(SO₄)₂]·H₂O structure. The crystal structure of [CsEu(H₂O)₃(SO₄)₂]·H₂O was determined by a single crystal X-ray diffraction analysis, and the crystal structure of CsEu(SO₄)₂ was obtained by the Rietveld method. [CsEu(H₂O)₃(SO₄)₂]·H₂O crystallizes in the monoclinic system, space group P2₁/c (a = 6.5574(1) Å, b = 19.0733(3) Å, c = 8.8364(2) Å, β = 93.931(1)°, V = 1102.58(3) Å3). The anhydrous sulfate CsEu(SO₄)₂ formed as a result of the thermal destruction crystallizes in the monoclinic system, space group C2/c (a = 14.327(1) Å, b = 5.3838(4) Å, c = 9.5104(6) Å, β = 101.979(3) °, V = 717.58(9) Å3). The vibration properties of the compounds are fully consistent with the structural models and are mainly determined by the deformation of non-rigid structural elements, such as H₂O and SO₄²⁻. As shown by the diffused reflection spectra measurements and DFT calculations, the structural transformation from [CsEu(H₂O)₃(SO₄)₂]·H₂O to CsEu(SO₄)₂ induced a significant band gap reduction. A noticeable difference of the luminescence spectra between cesium europium sulfate and cesium europium sulfate hydrate is detected and explained by the variation of the extent of local symmetry violation at the crystallographic sites occupied by Eu³⁺ ions, namely, by the increase in inversion asymmetry in [CsEu(H2O)₃(SO₄)₂]·H₂O and the increase in mirror asymmetry in CsEu(SO₄)₂. The chemical shift of the ⁵D₀ energy level in cesium europium sulfate hydrate, with respect to cesium europium sulfate, is associated with the presence of H₂O molecules in the vicinity of Eu³⁺ ion.

The oxidation reactions of BaLaCuS₃ in the artificial air atmosphere were studied at different heating rates in the temperature range of 50–1200 °C. The oxidation stages were determined by DSC-TG, XRD and IR–vis methods. The kinetic characteristics of the proceeding reactions were obtained with the use of the Kissinger model in a linearized form. Compound BaLaCuS₃ was stable in the air up to 280 °C. Upon further heating up to 1200 °C, this complex sulfide underwent three main oxidation stages. The first stage is the formation of BaSO₄ and CuLaS₂. The second stage is the oxidation of CuLaS₂ to La₂O₂SO₄ and copper oxides. The third stage is the destruction of La₂O₂SO₄. The final result of the high-temperature treatment in the artificial air atmosphere was a mixture of barium sulfate, copper (II) oxide and La₂CuO₄. The mechanism and stages of BaLaCuS₃ oxidation and further interactions of the components were discussed.

A new polymorphic modification of lanthanum sulfate was obtained by thermal dehydration of the respective nonahydrate. According to powder X-ray diffraction, it was established that β-La₂(SO₄)₃ crystallized in the C2/c space group of the monoclinic system with the KTh₂(PO₄)₃ structure type (a = 17.6923(9), b = 6.9102(4), c = 8.3990(5) Å, β = 100.321(3)°, and V = 1010.22(9) ų). Temperature dependency studies of the unit cell parameters indicated almost zero expansion along the a direction in the temperature range of 300–450 K. Presumably, this occurred due to stretching of the [LaO₉]_n chains along the c direction, which occurred without a significant alteration in the layer thickness over the a direction. A systematic study of the formation and destruction processes of the lanthanum sulfates under heating was carried out. In particular, the decisive impact of the chemical composition and formation energy of compounds on the thermodynamic and kinetic parameters of the processes was established. DFT calculations showed β-La₂(SO₄)₃ to be a dielectric material with a bandgap of more than 6.4 eV. The processing of β-La₂(SO₄)₃ with the Kubelka–Munk function exhibited low values below 6.4 eV, which indicated a fundamental absorption edge above this energy that was consistent with LDA calculations. The Raman and infrared measurements of β-La₂(SO₄)₃ were in accordance with the calculated spectra, indicating that the obtained crystal parameters represented a reliable structure.