Structural and magnetic properties of the ordered perovskite Pb2CoTeO6

Abstract: The complex perovskite Pb2CoTeO6 (PCTO) has been prepared as polycrystalline powders by solid state reaction route, and the crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, dielectric, calorimetric and magnetic measurements. It was shown that at room temperature this compound adopts a trigonal perovskite structure, space group R-3 (a= 5.6782(1){\AA}, c= 13.8552(3){\AA}). The compound undergoes a number of temperature-induced phase transitions and adopts four different structures in the temperature range 5-500 K: monoclinic in P21/n(5<T<125K, tilt system (a+b-b-)), monoclinic in I2/m (125<T<210 K, tilt system (a0b-b-)), rhombohedral in R-3 (210<T<370K, tilt system (a-a-a-)), and finally cubic in Fm-3m (above 370K without any tilting). These structural phase transitions are coupled to a change in the dielectric constant and the heat capacity around 210 and 370K. A long-range antiferromagnetically ordered state has been identified from neutron powder diffraction and magnetic studies at different temperatures. Magnetic diffraction peaks were registered below the transition at about 16 K and a possible model for the magnetic structure is proposed. Possible coexistence of long-range ordering of electrical dipoles and magnetic moments at low temperatures making PCTO a multiferroic candidate is discussed and compared with those of other Co-based quaternary oxides adopting the perovskite structure.