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Structural, dielectric, electrical and piezoelectric properties of Ba4SrRTi3V7O30 (R=Sm, Dy) ceramics

100%
Sahoo P., Panigrahi A., Patri S., Choudhary R.
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vol. 6
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issue 4
843-848
EN
Polycrystalline samples of Ba4SrRTi3V7O30 (R=Sm and Dy), members of the tungsten-bronze family, were prepared using a high-temperature, solid-state reaction technique and studied their electrical properties (using complex impedance spectroscopy) in a wide range of temperature (31–500°C) and frequency (1 kHz-1 MHz). Preliminary structural (XRD) analyses of these compounds show the formation of single-phase, orthorhombic structures at room temperature. The scanning electron micrographs (SEM) provided information on the quality of the samples and uniform distribution of grains over the entire surface of the samples. Detailed studies of the dielectric properties suggest that they have undergone ferroelectric-paraelectric phase transition well above the room temperatures (i.e., 432 and 355°C for R= Sm and Dy, respectively, at frequency 100 kHz). Measurements of electrical conductivity (ac and dc) as a function of temperature suggest that the compounds have semiconducting properties much above the room temperature, with negative temperature coefficient of resistance (NTCR) behavior. The existence of ferroelectricity in these compounds was confirmed from a polarization study.
2
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Dielectrophoretic mobility in the characterization of properties of microparticles

100%
Kuokkanen M.
Open Physics
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2010
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vol. 8
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issue 2
178-183
EN
The dielectric properties of microparticles were characterized by quadrupole electrode geometry. Quadruple microelectrode geometry with hyperbolic active interfaces was designed and fabricated. The dielectrophoretic mobility coefficients of the polystyrene microparticles were attained from negative dielectrophoresis. With the mobility coefficients and hypothetical inflection frequencies of the particles, the permittivity and electric conductivity of the particles in suspension were calculated. This demonstration established that dielectrophoretic mobility attained with a hyperbolic electrode can be used to characterize microparticle properties in suspension.
3
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Structural and electrical properties of KCa2Nb5O15 ceramics

100%
Behera B., Nayak P., Choudhary R.
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vol. 6
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issue 2
289-295
EN
A polycrystalline sample of KCa2Nb5O15 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°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°C) and frequency (102–106 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.
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