RESUMEN
Complex transition-metal oxides exhibit a wide variety of chemical and physical properties which are a strong function the local electronic states of the transition-metal centres, as determined by a combination of metal oxidation state and local coordination environment. Topochemical reduction of the double perovskite oxide, LaSrCoRuO6 , using Zr, yields LaSrCoRuO5 . This reduced phase contains an ordered array of apex-linked square-based pyramidal Ru3+ O5 , square-planar Co1+ O4 and octahedral Co3+ O6 units, consistent with the coordination-geometry driven disproportionation of Co2+ . Coordination-geometry driven disproportionation of d7 transition-metal cations (e.g. Rh2+ , Pd3+ , Pt3+ ) is common in complex oxides containing 4d and 5d metals. However, the weak ligand field experienced by a 3d transition-metal such as cobalt leads to the expectation that d7+ Co2+ should be stable to disproportionation in oxide environments, so the presence of Co1+ O4 and Co3+ O6 units in LaSrCoRuO5 is surprising. Low-temperature measurements indicate LaSrCoRuO5 adopts a ferromagnetically ordered state below 120â K due to couplings between S=1 /2 Ru3+ and S=1 Co1+ .
RESUMEN
CONTEXT: In this study, the authors have investigated the structural, optoelectronic, thermoelectric, and thermodynamic properties of Ca2NaIO6 and Sr2NaIO6 double perovskite oxides. Both materials exhibit semiconductor behavior with direct band gaps (Eg) of 0.353 eV and 0.263 eV, respectively. Optical parameters like absorption coefficient α(ω), reflectivity R(ω), dielectric constants, and refractive index have been calculated. The most notable absorption peaks are identified at 5.52 eV (equal to 108.33 × 104 cm-1) in the case of Ca2NaIO6 and at 11.16 eV (equivalent to 118.17 × 104 cm-1) for Sr2NaIO6. These findings suggest a promising outlook for applications in optoelectronics. Moreover, their commendably low thermal conductivity and a high figure of merit, particularly at low temperatures (100 K), indicate their effectiveness as thermoelectric materials. This analysis underscores that these materials hold potential as suitable candidates for n-type doping, making them well-suited for use in thermoelectric devices. Studying thermal properties, including thermal expansion, bulk modulus, acoustic Debye temperature, entropy, and heat capacity, contributes to understanding the materials' thermodynamic stability. The titled materials are dynamically stable. The analysis of these double perovskite materials highlights their potential across various technological applications due to their advantageous structural, electronic, optical, and transport properties, offering new possibilities in material science and technology development. METHODS: The study utilized the full potential linearized augmented plane wave (FP-LAPW) method in conjunction with density functional theory within the WIEN2k simulation code. This approach is widely recognized as one of the most dependable methods for evaluating the photovoltaic characteristics of semiconducting perovskites. The thermoelectric properties were ascertained using the rigid band approach and the constant scattering time approximation, both implemented in the BoltzTraP computational code.
RESUMEN
Double-perovskite oxide Sr2FeReO6 (SFRO) powders have promising applications in spintronics due to their half-metallicity and high Curie temperature. However, their magnetic properties suffer from the existence of anti-site defects (ASDs). Here, we report on the synthesis of SFRO powders by the sol-gel process. The B-site cationic ordering degree (η) and its influence on magnetic properties are investigated. The results demonstrate that the η value is well controlled by the annealing temperature, which is as high as 85% when annealing at 1100 °C. However, the annealing atmospheres (e.g., N2 or Ar) have little effect on the η value. At room temperature, the SFRO powders crystallize in a tetragonal crystal structure (space group I4/m). They have a relatively uniform morphology and the molar ratios of Sr, Fe, and Re elements are close to 2:1:1. XPS spectra identified that Sr, Fe, and Re elements presented as Sr2+, Fe3+, and Re5+ ions, respectively, and the O element presented as O2-. The SFRO samples annealed at 1100 °C in N2, exhibiting the highest saturation magnetization (MS = 2.61 µB/f.u. at 2 K), which was ascribed to their smallest ASD content (7.45%) with an anti-phase boundary-like morphology compared to those annealed at 1000 °C (ASDs = 10.7%) or 1200 °C (ASDs = 10.95%).