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Measurements of X-ray diffraction, electrical resistivity, and magnetization are reported across the Jahn–Teller phase transition in LaMnO3. Using a thermodynamic equation, we obtained the pressure derivative of the critical temperature (T JT ), dT JT /dP = −28.3 K GPa−1. This approach also reveals that 5.7(3)J (mol K)−1 comes from the volume change and 0.8(2) J (mol K)−1 from the magnetic exchange interaction change across the phase transition. Around T JT , a robust increase in the electrical conductivity takes place and the electronic entropy change, which is assumed to be negligible for the majority of electronic systems, was found to be 1.8(3) J (mol K)−1.

We have produced polycrystalline samples of Pr1-x Ba x MnO3 (0.0 ≤ x ≤ 0.5) through two different processes: (1) by mixing stoichiometric amounts of Pr oxide and carbonates of Mn and Ba (MO); and (2) through sol-gel precursors (SG). These samples were heat treated in air at several temperatures (500°C ≤ T ≤ 1400°C) and were characterized by X-ray powder diffraction, optical metallography, electrical resistivity ρ(T), and magnetoresistivity ρ(T, H). Results of X-ray powder diffraction revealed that all samples have the pereovskite-like structure and that MO samples are comprised of at least two phase: Pr1-x Ba x MnO3. Metallographic analysis confirmed this last result and revealed, in sample prepared via sol-gel route (SG), uniform morphologies and average grain size < 1 μm. Measurments of electrical resistivity ρ(T) revealed that the magnitude of μ increases with decreasing temperature until reaching a maximum value at T c, which is the long-range ferromagnetic ordering temperature of the system....

We report on synthesis and general physical properties of the solid solutions Nd1-x Ln x NiO3; Ln = Sm, Eu, Gd, Er, Yb; 0 ≤ x ≤ 1. The samples were prepared through sol-gel precursors and were subjected to heat treatments at temperatures T ≤ 1000°C under oxygen pressures as high as 70 atm. From the results of x-ray powder diffraction we have found that all samples studied crystallize in the GdFeO3-type orthorhombically distorted perovskite structure. Structural analysis of Nd1-x Ln x NiO3 compounds revealed that both the tolerance factor t and the Ni—O—Ni bond angle decrease with increasing Ln content. The latter is corrected with the temperature in which the Metal—Insulator (MI) transition develops in these compounds. Characterization of these materials through measurements of electrical resistivity revealed that all samples display the MI transition in a large range of temperature 200 K ≤ T ≤ 450 K. These results have enabled us to mapped out the Mi transition as a function of either the compos...