Browsing by Author "Mathur, N. D."

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    Investigation of the electrocaloric effect in a PbMg2/3Nb1/3O3-PbTiO3 relaxor thin film
    (American Institute of Physics, 2009-05) Correia, T. M.; Young, J. S.; Whatmore, Roger W.; Scott, J. F.; Mathur, N. D.; Zhang, Qi
    Permittivity measurements of a 0.93PMN-0.07PT thin film show a broad maximum near 35 °C, and an anomaly at the depolarizing temperature Td = 18 °C on heating only, suggesting a dipolar glass-relaxor phase transition. No structural phase transition at 18 °C is apparent from ferroelectric hysteresis loops taken on field cooling and field heating. These loops show the thermal hysteresis expected for ferroelectric relaxors, which has not hitherto been experimentally verified in PbMg2/3Nb1/3O3-PbTiO3 thin films. Our data suggest the intriguing possibility of a giant electrocaloric effect (ΔT = 9 K, ΔE = 720 kV cm−1) at and near room temperature.
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    Nanocoatings on micro- or nano-particles
    (Maney Publishing, 2009-11) Libor, Zsuzsanna; Zhang, Qi; Israel, C.; Mathur, N. D.
    In recent years, coating processes with nanoparticles have been investigated for the development of nanostructured materials. In this work we report the core-shell structures of micro-composites of SiO2/Ni, SiO2/Fe3O4, and nano-composites of BaTiO3/Fe3O4 and PZT/Fe3O4. These composites were prepared by an aqueous chemical synthesis method and characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy Dispersive X-Ray (EDX) analysis and Vibrating Sample Magnetometry (VSM) before and after incorporation into the core-shell structure. The composite core-shell structures were formed by the control of the surface charges of particles in aqueous solutions. A specific composite (SiO2/Ni, SiO2/Fe3O4 and BaTiO3/Fe3O4 and PZT/Fe3O4 nano-composites) can be produced by controlling the pH and the molar ratio of components. These magnetic composites can be potentially applied in wide range of fields such as micro-reactors, delivery vehicle systems, drug delivery systems and multiferroics.
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    PST thin films for electrocaloric coolers
    (Iop Publishing Ltd, 2011-04-07T00:00:00Z) Correia, T. M.; Kar-Narayan, S.; Young, J. S.; Scott, J. F.; Mathur, N. D.; Whatmore, Roger W.; Zhang, Qi
    Relaxor behaviour in a thin film of partially ordered PbSc0.5Ta0.5O3 (PST) was confirmed via slim P-E loops and the frequency dependence of the temperature at which the dielectric constant is maximum. Indirect measurements of the electrocaloric effect suggest that removing a field of 774 kV cm-1 yields a temperature change of -3.5 °C to -6.9 °C over a broad range of operating temperatures near room temperature (1-127 °C), with a correspondingly large refrigerant capacity of 662 J kg-1. In addition to low electrical hysteresis, there is negligible thermal hysteresis. PST thin films are therefore promising for EC cooling near room temperatu