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Structural and electrical properties of KCa2Nb5O15 ceramics

100%
Behera B., Nayak P., Choudhary R.
Open Physics
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2008
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vol. 6
|
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.
2
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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.
Open Physics
|
2008
|
vol. 6
|
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.
3
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Dielectric properties of Ba3Sr2DyTi3V7O30 ceramics

100%
Sahoo P., Panigrahi A., Patri S., Choudhary R.
Open Physics
|
2010
|
vol. 8
|
issue 4
639-642
EN
A polycrystalline sample, Ba3Sr2DyTi3V7O30, with tungsten bronze structure was prepared by a mixed-oxide method at high temperature (950°C). Preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound was studied by scanning electron microscopy. The dielectric anomaly at 321°C may be attributed to the ferro-paraelectric phase transitions. This was also confirmed from the appearance of a hysteresis loop. The nature of variation of the ac conductivity and value of activation energy at different temperature regions, suggest that the conduction process is of mixed-type (i.e., ionic-polaronic and space charge generated from the oxygen ion vacancies).
4
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A Method to Produce Linearly Polarized Positrons and Positronium Atoms with the J-PET Detector

81%
Mohammed M., Białas P., Curceanu C., Czerwiński E., Dulski K., Gajos A., Głowacz B., Gorgol M., Hiesmayr B., Jasińska B., Kisielewska D., Korcyl G., Kowalski P., Kozik T., Krawczyk N., Krzemień W., Kubicz E., Pawlik-Niedźwiecka M., Niedźwiecki S., Pałka M., Raczyński L., Raj J., Rudy Z., Sharma N., Sharma S., Shivani, Skurzok M., Silarski M., Wieczorek A., Wiślicki W., Zgardzińska B., Zieliński M., Moskal P.
Acta Physica Polonica A
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2017
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vol. 132
|
issue 5
1486-1489
EN
A method for creating linearly polarized positrons and ortho-positronium (o-Ps) atoms with the J-PET detector is presented. The unique geometry and properties of the J-PET tomography enable one to design a positron source such that the quantization axis for the estimation of the linear polarization of produced o-Ps can be determined on the event by event basis in a direction of the positron motion. We intend to use ²²Na or other β⁺ decay isotopes as a source of polarized positrons. Due to the parity violation in the beta decay, the emitted positrons are longitudinally polarized. The choice of the quantization axis is based on the known position of the positron emitter and the reconstructed position of the positronium annihilation. We show that the J-PET tomography is equipped with all needed components.
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