The low temperature specific heats of C-15 structure UOs2 and UOsIR have been measured in order to compare them with the systems NpOs2, a ferromagnet with TCurie = 7.9 K, and NpOsIr, newly discovered to be a spin fluctuation system with a specific heat γ of 375 mJ mol−1 K−2. The uranium compounds, with U—U separations of 3.25 Å, less than the Hill limit of 3.4 Å, show normal metallic behavior, with γ(UOs2) = 20 ± 2 mJ mol−1K−2 and γ(UOsIr) = 33 ± 3 mJ mol−1 K−2.
The oxidation of ZrAl3 in dry oxygen in the temperature range 865–1073 K obeys a logarithmic rate law in the first period of reaction. An activation energy of 214 kJ mol−1 has been estimated. Some time after this first period, depending on the temperature, the protective oxide film transforms to a porous one and the reaction rate increases. The oxide layer consists of α-Al2O3, tetragonal ZrO2 and small amounts of monoclinic ZrO2, in contrast to the ZrO2 oxide layer formed during oxidation of other phases in the Zr-Al system, where the selective oxidation of zirconium takes place.
The IR absorption spectra of tetragonal copper manganite CuxMn3−x O4 spinels (O < x < 1) have singled out a discontinuity in cation distribution to occur at x > 0.60 in conformity with that recorded by our previous measurements and have warranted the existence of a more complex cation distribution than that proposed earlier. It has been concluded from this study that the ionic configuration for x <0.60, i.e. (Cux+Mn1−x2+)A (Mn2−x3+Mnx4+)BO42−, changes for x > 0.60 to (Cux−y+Mn1−x+y2+)A(Cuy2+Mn2−x−y3+Mnx4+)BO42−, where y represents a low value (less than 0.20).
When the oxidation of Mn2+ and Cu+ ions is achieved below 450 °C, IR absorption measurements confirm the formation of a cation-deficient metastable spinel phase Cu1.5Mn1.5O4+δ with a 1:3 octahedral superstructure.
The system Ce-Sn has been reinvestigated in the temperature range from 400 to 800 °C using X-ray powder diffraction techniques. From a characterization of its crystal structures the existence of nine binary compounds has been confirmed.
Magnetic investigation of the binary cerium stannides in the temperature range from 4.2 to 600 K revealed a systematic tendency for ferromagnetic ordering of the ceriumrich compounds up to a ratio Ce:Sn ≈ 1, followed by antiferromagnetism up to a ratio of Ce:Sn ≈ 0.4, towards interconfigurational fluctuation in the compound richest in tin, CeSn3. Candidates for heavy fermion behaviour found in the transition regions, besides CeSn3, are α-Ce5Sn3 and Ce11Sn10.
The compounds RFe12−xRex (R Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y, Th, U) were synthesized at the nominal composition x = 2 by arc melting from the elements followed by annealing. The poly crystalline samples were examined by X-ray powder diffraction and magnetization measurements. They all crystallize with a partially substituted tetragonal ThMn12-type structure and are magnetically ordered with Curie temperatures in the range Tc = 340(U)-475(Sm) K and magnetic moments at 4.2 K in the range 8.0(Dy)–21.4(Nd) μB per formula unit. Atomic coordinates are given for two members with refined compositions, PrFe10.5Re1.5 and GdFe10.6Re1.4.
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