Micro-Raman Spectra of YBaCuO Superconductors

A systematic study of the Raman spectra of Y-Ba-Cu-O superconducting materials under different experimental conditions clarifies the controversial results given in the literature. Under the determined conditions and thanks to the micro-Raman technique, reproducible polarized Raman spectra can be obtained and a coherent assignment can be suggested for YBa2Cu307and EuBa2Cu307.For YBa2Cu3(OjF);, the introduction of fluorine atoms was found to be localized in pyramidal CuO units rather than in CuO chains

Micro-Raman Spectra of YBaCuO Superconductors

A systematic study of the Raman spectra of Y-Ba-Cu-O superconducting materials under different experimental conditions clarifies the controversial results given in the literature. Under the determined conditions and thanks to the micro-Raman technique, reproducible polarized Raman spectra can be obtained and a coherent assignment can be suggested for YBa2Cu307and EuBa2Cu307.For YBa2Cu3(OjF);, the introduction of fluorine atoms was found to be localized in pyramidal CuO units rather than in CuO chains

Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites

The topotactic phase transition in SrCoOx (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO2.5, however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoOx is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions

Investigation of the SrFe1-xCoxO3 (0≤x≤1) Cubic Perovskites Obtained by Electrochemical Oxidation

The transition-metal perovskites SrFe1-xCoxO3 (0≤x≤1) are of a great interest because the high oxidation states of the transition-metal (Fe(IV), Co(IV)) can be stabilized. Moreover these compounds exhibit interesting magnetic properties. These oxygen stoichiometric phases have been prepared only under high oxygen pressures. A novel preparation method of these phases has been investigated using electrochemical oxidation of the SrFe1-xCoxO2.5 brownmillerite-type compounds [1-3]. The starting materials and the phases obtained after electrochemical processing have been characterized by X-ray powder diffraction, chemical analysis and 57Fe Mössbauer spectroscopy. Finally, the magnetic and transport properties have been studied