ABSTRACT
The complex perovskite Pb(2)CoTeO(6) (PCTO) has been prepared as polycrystalline powders by a 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 R3 (a = 5.6782(1) Å, c = 13.8552(3) Å). The compound undergoes a number of temperature-induced phase transitions and adopts four different structures in the temperature range 5-500 K: monoclinic in P2(1)/n (5 < T < 125 K, tilt system (a(+)b(-)b(-))), monoclinic in I2/m (125 < T < 210 K, tilt system (a(0)b(-)b(-))), rhombohedral in R3 (210 < T < 370 K, tilt system (a(-)a(-)a(-))), and finally cubic in Fm3m (above 370 K without any tilting). These structural phase transitions are coupled to changes in the dielectric constant and the heat capacity around 210 and 370 K. 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 the electrical dipoles and the magnetic moments at low temperatures making PCTO a potential multiferroic candidate is discussed.
ABSTRACT
The complex perovskite Ba(2)CoTeO(6) (BCTO) has been synthesised, and the crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy and dielectric, calorimetric and magnetic measurements. It is shown that at room temperature this compound adopts the 6L-trigonal perovskite structure, space group P3[combining macron]m (s.g. 164) (a = 5.7996(1) A, c = 14.2658(3) A). The structure comprises dimers of face-sharing octahedra as well as octahedra which share only vertices with their neighbours. Dielectric measurements indicate a diffuse transition of antiferroelectric nature near 280 K. A long-range antiferromagnetically ordered state has been identified from neutron diffraction and magnetic studies. The magnetic diffraction peaks were registered below the magnetic transition at about 15 K and a possible model for the magnetic structure is proposed. The structural and magnetic features of this compound are discussed and compared with those of other Co-based quaternary oxides adopting the perovskite structure.
ABSTRACT
The deformation electron density of the urea-phosphoric acid adduct has been studied from 100 K X-ray and neutron diffraction experiments. Data were interpreted according to the Hirshfeld model. The long hydrogen bonds show characteristics of electrostatic interaction. Deformation density maps on the short hydrogen bond shows hydrogen more strongly bonded to urea than to phosphoric acid, and peak maxima at almost midway between the two O-H bonds.
