Effect of MoO₃ and TiO₂ Powder Particle Sizes on the Phase Composition and Density of Dysprosium Titanate Pellets

An important process task is to expand the range of raw materials applied for the synthesis of dysprosium titanate (neutron-absorbing material for VVER-1000 reactors) and to establish and optimize methods for producing powders and pellets with characteristics that meet specific technical requirements, primarily those for the density and structural and phase compositions of the materials. The influence of MoO₃ doping additions and TiO₂ powders with different particle sizes on the density and phase composition of dysprosium titanate (Dy₂O₃ · TiO₂) pellets was experimentally studied. Titanium oxide powders of two grades were used: powder with spherical 10–30 μm particles (OSCh 7-3 grade as per TU 6-09-3811–79) and powder with an average particle size of ~63 nm (China Rare Metal Material Co., China). The nanosized TiO₂ powder intensified the sintering of the pellets, which achieved a density of 6.9 g/cm³ and acquired a single-phase hexagonal structure at 1650°C. The coarse TiO₂ powder did not promote high density of the sintered pellets, nor did it facilitate complete synthesis of dysprosium titanate since a significant amount of intermediate dysprosium dititanate (Dy₂Ti₂O₇) and initial dysprosium oxide (Dy₂O₃) remained in the synthesized material. The introduction of MoO₃ intensified the sintering of pellets, increased the pellet density up to 6.7 g/cm³, and led to a single-phase cubic structure of pyrochlore type, regardless of the TiO₂ powder grade. The simultaneous use of the nanosized TiO₂ powder and MoO₃ doping addition increased the density of the sintered dysprosium titanate pellets to 7.1 g/cm³ and promoted a single-phase structure of pyrochlore type.