The rare earth iron garnets R3Fe5O12（R=Sm, Eu） were synthesized under mild hydrothermal conditions, and their crystal growth was found to be sensitive to alkalinity, reaction temperature and time. The as-prepared samples were characterized by powder X-ray diffraction（XRD）, scanning electron microscopy（SEM）, infrared spectra（IR） and Raman spectrum. The M vs. H loops and magnetic parameters have been traced with a vibrating sample magnetometer（VSM） and superconducting quantum interference devices（SQUIDs） magnetometer. We proposed the formation mechanisms and formulated a reasonable explanation for their growth habits. Different morphologic characteristics were observed by changing alkalinity in the reaction systems. The magnetic studies gave saturation magnetization（Ms） and Curie temperature（TC）. The magnetic behaviors of Sm3Fe5O12 and Eu3Fe5O12 in mild hydrothermal systems are comparable with those in high temperature solid state reactions.
GUO Li YUAN Hong-ming HUANG Ke-ke YUAN Lin LIU Shao-kong FENG Shou-hua
Rare earth iron garnets R3Fe5-xMnxO12（R=Pr, Nd, Sm, Eu） were prepared through mild hydrothermal me- thod. The initial alkalinity of solutions was thought to play an important role in governing the content of Mn. The effect of substitution Fe^3＋ ions by Mn^3＋ ions on magnetic properties was investigated. The saturation magnetizations of Mn-doped samples are larger than that of corresponding parent compounds due to the moment of Mn^3＋ ion being smaller than that of Fe^3＋. It is clearly shown that incorporation of Mn^3＋ gives rise to significant variations in the Curie temperature. With increasing of Mn content x, Curie temperatures reduced sharply for the garnets, which could be explained by the exchange interaction between a-d Fe^3＋ being reduced in these compounds.
The powder crystals of RMnO3（R=Er, Tm） with hexagonal and orthorhombic structures were prepared under hydrothermal conditions. The different structural phases of the title compounds were controllably formed from different kinds of precursors at different reaction temperatures. All of the samples were characterized by powder X-ray diffraction, scanning electron microscopy, inductively coupled plasma analysis, and variable temperature magnetic susceptibility. Their structures were refined by Rietveld method from powder X-ray diffraction data. The measurement of magnetic behavior shows antiferromagnetic orderings at Neel temperatures around 80 and 40 K for the hexagonal and orthorhombic phases, respectively.
A series of double perovskites RSrMnFeO6（R=La, Pr, Nd, Sm） was synthesized under mild hydrothermal conditions. Crystal growths of the samples were sensitive to alkalinity, temperature, filling fraction, and composition of initial reaction mixture. The desired series of compounds belongs to the class of AA＇BB＇O6 perovskites with a random distribution of Mn and Fe atoms over the B-cation sub-lattice. Their structures show the distorted orthorhombic symmetry with space group Pnma. The shapes and sizes of the crystals were analyzed on a Rigaku JSM-6700F by scanning electron microscopy. Analysis done by XPS, Mossbauer spectroscopy and iodometric titration reveals that Mn and Fe ions have ＋4 and ＋3 oxidation states, respectively.
ZHANG Gang-hua YUAN Hong-ming CHEN Yan LI Wei-juan YANG Mei-qi FENG Shou-hua
A double perovskite oxide Ba2FeSbO6 was hydrothermally synthesized and structurally characterized by X-ray diffraction. This solid compound shows a single phase and has a trigonal structure with space group R3 ？m and cell parameters of a=0.57261 nm and c=1.40244 nm. The dielectric constant and loss tangent of the solid measured in a frequency range from 100 Hz to 1 MHz at temperatures from 313 K to 513 K reveal a relaxation process of frequency dependence of the real part（ε＇） of dielectric constant and dielectric loss tan？. The frequency dependence of electrical property led to the framework of conductivity and electric modulus formalisms. The scaling behavior of imaginary part of electric modulus suggests that the relaxation describes the single mechanism at various temperatures. The variation tendency of the alternating current impedance indicates the thermally activated conduction process follows Jonsche＇s power law.
LI MinYUAN Hong-mingXU WeiHAN MeiYAO Lin-ranYANG MingFENG Shou-hua
Polycrystallines Bi0.5Ca0.5-xLaxFe0.3Mn0.7O3（x=0, 0,05, 0.10, 0.15, 0.20, 0.25） were prepared by molten salt method and showed perovskite orthorhombic structure with space group Pnma. The magnetic measurements indicate that the compounds exhibit antiferromagnetic behavior in a temperature range of 4-300 K. The measurements of transport properties suggest that the substitution of La for Ca enhanced the conductivity, and a kink appeared on the curve of temperature dependence of resistivity at 275 K, which is related to the spin-reorientation in the samples.
DONG Zhong-ping HU Bin CHEN Yan YUAN Hong-ming FENG Shou-hua
