RESUMO
Binary Cu x O1-x compounds have some advantages as optoelectronic functional materials, but their further development has encountered some bottlenecks, such as inaccurate bandgap values and slow improvement of photoelectric conversion efficiency. In this work, all possible stoichiometric ratios and crystal structures of binary Cu x O1-x compounds were comprehensively analyzed based on a high-throughput computing database. Stable and metastable phases with different stoichiometric ratios were obtained. Their stability in different chemical environments was further analyzed according to the component phase diagram and chemical potential phase diagram. The calculation results show that Cu, Cu2O and CuO have obvious advantages in thermodynamics. The comparison and analysis of crystal microstructure show that the stable phase of Cu x O1-x compounds contains the following two motifs: planar square with Cu atoms as the center and four O atoms as the vertices; regular tetrahedron with O atoms as the center and four Cu atoms as the vertices. In different stoichiometric ratio regions, the electron transfer and interaction modes between Cu and O atoms are different. This effect causes energy differences between bonding and antibonding states, resulting in the different conductivity of binary Cu x O1-x compounds: semi-metallic ferromagnetic, semiconducting, and metallicity. This is the root of the inconsistent and inaccurate bandgap values of Cu x O1-x compounds. These compositional, structural, and property variations provide greater freedom and scope for the development of binary Cu x O1-x compounds as optoelectronic functional materials.
RESUMO
Ni-Zn ferrites Ni(x)Zn1-xFe2O4 (x = 0.2, 0.4, 0.5, 0.6, 0.8) powders were synthesized by sol-gel technique. Structural, infrared and magnetic properties of samples were investigated. Spinel structural characteristics are shown by XRD spectra and the morphologies observed by atomic force microscopy demonstrate the samples are in nano-range. For all the samples, FTIR spectra exhibit obvious v1 infrared absorbing bands, in the range 500-600 cm-1, corresponding to intrinsic stretching vibrations of the metal ions at the tetrahedral site (Td), Mtetra <--> O. Furthermore, the central position of v1 band is tending to shift to larger wave numbers with the increasing Ni contents in the samples. For the samples Ni(x)Zn1-xFe2O4 (x = 0.2, 0.4), the v2 infrared absorbing bands, in the range 450-385 cm(-1), corresponding to stretching vibrations of the metal ions at the octahedral-metal stretching (Oh), Mocta <--> O, were also observed. However, for samples Ni(x)Zn1-xFe2O4 with higher Ni content (x = 0.5, 0.6, 0.8), the v2 infrared absorbing bands were obscure. The magnetic hysteretic loops at room temperature obtained from vibration samples magnetometer reveal the soft magnetism of the samples. The sample with lowest Ni content, Ni0.2Zn0.8Fe2O4, presents much higher saturation field than the other samples. The coercive field rises with increased Ni content, which is ascribed to the increased magnetocrystalline anisotropy constant with Ni content.
