RESUMO
The vibrational and optical properties of an La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 (LSNMT) polycrystalline sample produced via a solid-state reaction were studied. The Raman spectrum at room temperature reveals the chemical disorder in our compound. The optical gap and Urbach energy were estimated on the basis of the absorption spectrum. Moreover, the polycrystalline manganite radiates in the near-infrared light (1000 nm) with 514.5 nm light excitation and in the temperature range from 10 K to 300 K. Crystal field analysis suggests that only the Mn4+ luminescent center is found in LSNMT. The measured activation proves that our compound possesses good thermostability. The chromaticity coordinates prove that the emission of the LSNMT sample occurs in the near-infrared region. All analytical findings demonstrate that LSNMT manganite has substantial prospective applications in white luminescent devices.
RESUMO
In the present work, structural and dielectrics properties of polycrystalline sample Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 (BBTZN) prepared by a molten-salt method were investigated. X-ray diffraction analyses revealed the formation of a single-phase pseudocubic structure with a Pm3Ìm space group. Unlike the trend observed in classic ferroelectrics, the temperature dependence of the dielectric constants showed the presence of three sequences of structural phase transitions. In fact, the local disorder provides a frequency dependent relaxor like behaviours attributed to the dynamic of polar nanoregions (PNRs). The diffuse phase transition (DPT) analyzed using the modified Curie-Weiss law and Lorenz formula confirms the presence of short-range association between the nanopolar domains. The obtained values of the degree of diffuseness are found to be in the range of 1.58-1.78 due to the existence of different states of polarization and, hence, different relaxation times in different regions. The frequency dependence of temperature at dielectric maxima, which is governed by the production of PNRs at a high temperature, satisfies the Vogel-Fulcher (V-F) law. The temperature dependence of the electric modulus for various frequencies indicating a thermally activated relaxation ascribed to the Maxwell-Wagner (M-W) space charge relaxation phenomenon.
RESUMO
The dielectric properties of Ca0.85Er0.1Ti1-x Co4x/3O3 (CETCo x ) (x = 0.00, 0.05 and 0.10), prepared by a sol-gel method, were systematically characterized. The temperature and frequency dependence of the dielectric properties showed a major effect of the grain and grain boundary. The dielectric constant and dielectric loss of CETCo x decreased sharply with increasing frequency. This is referred to as the Maxwell-Wagner type of polarization in accordance with Koop's theory. As a function of temperature, the dielectric loss and the real part of permittivity decreased with increasing frequency as well as Co rate. Indeed, a classical ferroelectric behavior was observed for x = 0.00. The non-ferroelectric state of the grain boundary and its correlation with structure, however, proved the existence of a relaxor behavior for x = 0.05 and 0.10. The complex electric modulus analysis M*(ω) confirmed that the relaxation process is thermally activated. The normalized imaginary part of the modulus indicated that the relaxation process is dominated by the short range movement of charge carriers.
