Abstract
LaTiO3.5 crystals were grown by optical floating zone technique in air, O₂ or Ar. Crystal structure varies between orthorhombic Pna2₁ (air, O₂) and monoclinic P2₁ (Ar). Crystals are transparent (air, O₂) or opaque (Ar) with amber or black colour. Magnetization resembles properties of LaTiO_3.5. (Dy_xLa_1–x)₂Ti₂O₇ crystals were grown in O₂. The solubility of dopant (La or Dy) in the parent compound is limited. Two phases with Pna2₁ and Fd¯3m structure coexist in the range from x = 0.32 to 0.68. The a-axis of Pna2₁ is intact by substitution of La³⁺ by Dy³⁺; both b- and c-axis decreases. The a-axis of Fd¯3m increases with substitution of Dy³⁺ by La³⁺ and the spin freezing temperature T_f shifts to higher temperature. Either of new magnetic phase (Pna2₁ structure) or dynamical behaviour of spins in Fd¯3m phase exists below x = 0.68 in the range between transition to ‘spin ice’ state T_i and T_f.

Key words
optical floating zone, single crystals, crystal structure, ferroelectrics, spin ice

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