A novel perovskite‐like Ta‐bronze KTa 1+ z O 3 : preparation, stoichiometry, conductivity and crystal structure studies

A new cubic Ta‐bronze (1) KTaO 3 [ z ≃ 0.107 (3)] was obtained on a cathode by molten salt electrolysis of the system K 2 TaOF 5 –K 3 TaO 2 F 4 –(KF + NaF + LiF) eutectic . Black, metallic cubic crystals of (1) are formed together with tetragonal β‐Ta. The perovskite‐like crystal structure of (1) [ a = 4.005 (1) Å, space group ] was refined with anharmonic displacement parameters for Ta and K atoms and anisotropic displacement parameters for a split O‐atom position [KM4CCD diffractometer; λ(Mo K α); 3320 measured reflections with I > 3σ( I ); R = 0.0095, wR = 0.0065, Δρ min = −0.91 e Å −3 , Δρ max = 0.65 e Å −3 ]. Defects in the O and K atomic positions were found. (1) is a semiconductor in the temperature range 4–300 K, whereas the well studied and closely related colourless transparent crystals KTa +5 O 3 (2) are dielectric. Differences in the properties of (1) and (2) are assumed to be connected with the existence of Ta dumb‐bells statistically distributed into the KTaO 3 matrix.