High-pressure synthesis, crystal structure and magnetic properties of TlCrO3 perovskite

Abstract

TlMO₃ perovskites (M³⁺ = transition metals) are exceptional members of trivalent perovskite families because of the strong covalency of Tl³⁺–O bonds. Here we report on the synthesis, crystal structure and properties of TlCrO₃ investigated by Mössbauer spectroscopy, specific heat, dc/ac magnetization and dielectric measurements. TlCrO₃ perovskite is prepared under high pressure (6 GPa) and high temperature (1500 K) conditions. The crystal structure of TlCrO₃ is refined using synchrotron X-ray powder diffraction data: space group Pnma (no. 62), Z = 4 and lattice parameters a = 5.40318(1) Å, b = 7.64699(1) Å and c = 5.30196(1) Å at 293 K. No structural phase transitions are found between 5 and 300 K. TlCrO₃ crystallizes in the GdFeO₃-type structure similar to other members of the perovskite chromite family, ACrO₃ (A³⁺ = Sc, In, Y and La–Lu). The unit cell volume and Cr–O–Cr bond angles of TlCrO₃ are close to those of DyCrO₃; however, the Néel temperature of TlCrO₃ (T_N ≈ 89 K) is much smaller than that of DyCrO₃ and close to that of InCrO₃. Isothermal magnetization studies show that TlCrO₃ is a fully compensated antiferromagnet similar to ScCrO₃ and InCrO₃, but different from RCrO₃ (R³⁺ = Y and La–Lu). Ac and dc magnetization measurements with a fine step of 0.2 K reveal the existence of two Néel temperatures with very close values at T_N2 = 87.0 K and T_N1 = 89.3 K. Magnetic anomalies near T_N2 are suppressed by static magnetic fields and by 5% iron doping.