Hirohisa Satoh

Heat capacities of LnCrO3 (Ln=rare earth)

Abstract The heat capacities of LnCrO 3 (LnLa, Pr, Nd, Sm, Gd, Dy, Ho, Er and Y) were measured by differential scanning calorimetry (DSC) from 150 to 450 K and also alternating current calorimetry (ACC) from 77 to 280 K. Thermal anomalies due to magnetic transition were observed in all of the heat capacities of LnCrO 3 . The transition temperature and the enthalpy changes depend on rare earth elements. On the other hand, the entropy changes do not depend on ionic radii of the rare earth element. Thermodynamic functions of LnCrO 3 (LnDy, Ho and Y) are calculated above room temperature.

Growth and structure analysis of single crystal of tetragonal BaGd2Mn2O7 with a superlattice structure

Abstract Single crystal of BaGd 2 Mn 2 O 7 was grown by the floating zone method, and its crystal structure was determined using single crystal X-ray method. This compound has the ordered structure of tilting oxygen octahedron surrounding a central manganese ion (space group P4 2 /mnm). The lattice constants are a =0.55374(8), c =2.0618(1) nm and Z =4. The oxygen octahedron surrounding a central manganese ion is slightly distorted and mutually tilts between the neighboring oxygen octahedrons with an angle of several degrees. These single crystal data confirmed our previous results from the Rietveld analysis of powder X-ray diffraction patterns [J. Alloys Compd. 311 (2000) 69].

Further study on the phase transition of BaTb2Mn2O7

Abstract The electrical conductivity of the orthorhombic BaTb2Mn2O7 phase has been measured as a function of temperature from room temperature to 1273K. The electrical conductivity exhibits an irregular behavior at 755K. The Differential Scanning Calorimeter (DSC) measurement also shows a thermal anomaly at 745K in the heating step, although thermal hysteresis was found. These results from both experiments indicate the occurrence of a phase transition near these temperatures. The transition temperatures determined in this work are a little higher than that from high temperature X-ray diffractometry. The enthalpy change for the phase transition is 3.0 KJ mol−1, a little higher than the values of BaEu2Mn2O7 and BaSm2Mn2O7.

Phase transition of the Ca1.5Nd0.5MnO4 phase

Abstract From the results of high temperature X-ray diffractometry, it has been found that Ca 1.5 Nd 0.5 MnO 4 phase has a phase transition from orthorhombic to tetragonal. The transition temperature, near 320 K, is determined by DSC, electrical conductivity and magnetic susceptibility measurements. Ca 1.5 Nd 0.5 MnO 4 phase has an orthorhombic structure when it is annealed under low oxygen partial pressure at high temperature, while it has tetragonal structure when annealed under high oxygen partial pressure, although the degree of oxygen nonstoichiometry is small.

Another type of orthorhombic distortion in BaGd2Mn2O7 phase

Abstract A new type of orthorhombic phase was found in BaGd 2 Mn 2 O 7 by thermal cycling above and below the transition temperature, which is considered the true equilibrium phase. This distortion is usually typical of the orthorhombic phase in BaSm 2 Mn 2 O 7 or BaEu 2 Mn 2 O 7 compound.

Superstructure of tetragonal BaGd2Mn2O7

Abstract The crystal structure of a layered perovskite compound, BaGd 2 Mn 2 O 7 , was analyzed for the powder X-ray diffraction data by Rietveld method. The tetragonal BaGd 2 Mn 2 O 7 phase has superlattice lines so that the space group of P4 2 /mnm (No. 136) was determined with the unit cell dimensions a =0.55024(1) and c =2.02457(5) nm. The MnO 6 octahedron was distorted and tilts by 6° apart from the c axis mutually in the reverse direction.

Stability of phases in (Ba, Gd)MnO3 solid solution system

Abstract The existing phases in Ba x Gd 1-x MnO 3 solid solution system (0 ≦ x ≦ 1) were studied by analyzing the detailed crystal structure of each composition from the results of the Rietveld method using powder X-ray diffraction data. For a small substitution of Ba for Gd (0 ≦ x Pnma space group) was stably formed and this fact was supported by the electron diffraction data. There existed an intermediate phase of Ba 0.33 Gd 0.67 MnO 3 , which was characterized as the tetragonal phase with perovskite structure. The composition range of this phase was narrow and almost line compound. Between the regions of these phases, there existed two-phase region. There was also a two-phase region between the intermediate tetragonal phase and BaMnO 3 . Measurement of electrical conductivities of these orthorhombic solid solutions and tetragonal phases showed semiconducting behaviors for both phases and the existence of the phase transition at high temperature for the orthorhombic phase. The transition temperature decreased as the Ba content increased.

Crystal growth and structural analysis of PrMnO3 and TbMnO3

Single crystals of PrMnO3 and TbMnO3 were grown by floating zone method and the crystal structure was determined by single crystal X-ray diffractometry. The structure of these compounds belongs to the orthorhombic system (space group is Pnma, No. 62) with the lattice parameters alpha approximate to root (.) - a(p), b approximate to 2 (.) a(p) , c approximate to root 2.a(p) and Z = 4, where a(p) is ideal cubic perovskite cell parameter.

Structural phase transition in the layered perovskite compound BaTb2Mn2O7

A distorted layered perovskite compound BaTb2Mn2O7 was synthesized by the solid state reaction in pure argon. There is a structural phase transition in the BaTb2Mn2O7 compound. The phase transition was characterized by the DSC and high temperature Xray diffraction. The heat capacity of BaTb2Mn2O7 was calculated. The thermal anomaly corresponding to the phase transition was observed at about 740K. The lattice parameters were calculated by the CELL program for BaTb2Mn2O7, It has Tb-type orthorhombic symmetry with a = 0.3908 nm, b = 0.3866 nm, c = 2.0163 nm, and space group Immm at room temperature. With the increase of temperature, the lattice parameters gradually increase until 673K. From 723K to 973K, the compound translates to tetragonal with a = 0.39078 nm, c = 2.0277 nm and S.G. I4/mmm. This result is fairly in accordance with that of heat capacity.