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

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 Mossbauer 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)angstrom, b = 7.64699(1)angstrom and c = 5.30196(1) angstrom 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, ACrO(3) (A(3+) = 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 Neel 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 anti-ferromagnet 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 Neel temperatures with very close values at T-N2 = 87.0 K and T-N1 = 89.3 K. Magnetic anomalies near TN2 are suppressed by static magnetic fields and by 5% iron doping.