Structural and electrical properties of KCa2Nb5O15 ceramics

Abstract

Abstract:A polycrystalline sample of KCa 2 Nb 5 O 15 with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105 0 C), which was confirmed by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31-500 0 C) and frequency (10 2 -10 6 Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers. A possible 'hopping' mechanism for electrical transport processes in the system is evident from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits Arrhenius type of electrical conductivity.

Synthesis and characterization of La 0.75 Ca 0.15 Sr 0.05 Ba 0.05 MnO 3 –Ni 0.9 Zn 0.1 Fe 2 O 4 multiferroic composites

“…The higher values of Z′ at lower frequencies means the polarization in the composites is larger. The merger of Z′ at higher frequencies indicates possible release of space charge polarization/ accumulation at the boundaries of homogeneous phases in the composites under the applied external field[66,67]. Our results are in well agreement with the reported results in BaTiO 3 /La 0.7 Ca 0.3 MnO 3 and (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 -PVDF composites…”

Investigation of complex impedance and modulus properties of Nd doped 0.5BiFeO3-0.5PbTiO3 multiferroic Composites

“…The frequency-temperature dependence of ac conductivity is shown in Figure 11(a-d). This figure shows that the conductivity for the concentration x=0.10, 0.15, 0.20 exhibit step like decrease in low frequency region suggest low frequency polarization which may be due to the transition from the bulk to contact resistance [28]. There is a deviation in the slope at a particular frequency usually called hopping frequency.…”

“…This behavior shows that the conduction mechanism increases with increasing temperature and frequency (i.e., negative temperature coefficient of behavior like that of a semiconductor). The coincidence of the value of Z at higher frequencies at all the temperatures indicates a possible release of space charge [28,29] and the frequency at which the release of space charge occurs also depends upon the Nd concentration. The space charge polarization occurs maximum at higher frequency side for x=0.20 concentration as compared to all other concentration.…”

Magnetic, Dielectric and Complex Impedance Properties of xBa0.95Sr0.05TiO3–(1 − x)BiFe0.9Gd0.1O3 Multiferroic Ceramics

“…It is also observed that the value of Z 0 for all compositions coincides at higher frequencies. The merger of Z 0 at higher frequencies indicates possible release of space charge polarization [39]. Variation of Z 0 with frequency at different temperatures (150-300°C) for the composition x = 0.25 is shown in Fig.…”