Nanopowders of lanthanum and yttrium orthophosphates have been synthesized. The growth of nanocrystals has been investigated in the temperature range 200–1100°C. The temperature-concentration limits...

One of the most critical problems for phosphors used in light-emitting diodes (LEDs) is the thermal quenching of luminescence. Herein, novel (Y_1−xEu_x)₂(SO₄)₃ (x = 0, 0.17, 0.33, 0.5, 0.66) phosphors with anti-thermal quenching of luminescence due to giant negative thermal expansion were obtained by crystallization from aqueous solutions. The Y₂(SO₄)₃ crystal structure is described as a framework, which consists of corner-sharing SO₄ tetrahedra and YO₆ octahedra. Thermal expansion of x = 0, 0.17, 0.5 solid solutions was investigated by high-temperature powder X-ray diffraction. The crystal structure of the x = 0.5 solid solution was refined by the Rietveld refinement using X-ray powder diffraction data at 400 and 500 °C to R_B = 1.7 and 1.9%, respectively. The rotation of the SO₄ tetrahedra results in giant negative volumetric thermal expansion: the structure contracts in all directions (α_a = −7(3), α_b = −15(3), α_c = −22(2), α_V = −44(2) · 10⁻⁶ °C⁻¹ at 500 °C for YEu(SO₄)₃). The photoluminescence intensity is enhanced 1.8 times with the temperature increasing up to 500 °C. The anti-thermal quenching of Eu³⁺ luminescence can be described in terms of thermal-enhanced energy transfer between Eu³⁺ ions due to the negative thermal expansion of the Y₂(SO₄)₃ matrix in all non-equivalent directions.

Nanosized precursor powders of (1 – x)ZrSiO₄‒xZrO(OH)₂ are synthesized by the sol-gel method with the separate precipitation of components to obtain (1 – x)ZrSiO₄‒xZrO₂ ceramic composites. The thermal behavior of precursor powders is studied by differential scanning calorimetry and thermogravimetry (DSC/TG). Ceramic composites with a high level of microhardness are obtained by sintering powders, preliminarily calcined at 850°C, in air in the temperature range 1000‒1300°C. In the future, such ceramic composites can be used as matrices for solidification and isolating high-level waste (HLW).

A group of phyllosilicate nanoscrolls conjoins several hydrosilicate layered compounds with a size mismatch between octahedral and tetrahedral sheets. Among them, synthetic Mg₃Si₂O₅(OH)₄ chrysotile nanoscrolls (obtained via the hydrothermal method) possess high thermal stability and mechanical properties, making them prospective composite materials fillers. However, accurate determination of these nano-objects with Young’s modulus remains challenging. Here, we report on a study of the mechanical properties evolution of individual synthetic phyllosilicate nanoscrolls after a series of heat treatments, observed with an atomic force microscopy and calculated using the density functional theory. It appears that the Young’s modulus, as well as shear deformation’s contribution to the nanoscrolls mechanical behavior, can be controlled by heat treatment. The main reason for this is the heat-induced formation of covalent bonding between the adjacent layers, which complicate the shear deformation.