Browsing by Author "Correia, T. M."

Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen Access
    Characterisation of lead barium zirconate thin films for utilisation of the electrocaloric effect
    (Elsevier, 2016-05-09) Shaw, Christopher P.; Zhang, Qi; Correia, T. M.; Weaver, P. M.
    Characterisation of a composition of Lead Barium Zirconate thin films deposited by a spin coating sol-gel process onto platinised silicon substrates has been undertaken to investigate a potential application utilising the reported electrocaloric properties of the material. Xray diffraction studies revealed that above 700 °C the presence of pyrochlore phase was replaced by ferroelectric phase but the identification of antiferroelectric phases previously reported could not be identified. Wet etching of the films produced an insoluble residue containing only evidence of zirconium out of the original three metals, which resembled a skeletal structure similar to the original rosette morphology of the annealed films. Elemental analysis of the annealed films using EDX indicated a non-target Pb:Ba:Zr ratio, which suggested a reduced Zr content of the films. “Solution-like” rather than “sol-like” nature of the spin coated sol and phase boundary proximity are proposed for reported observations, and a mechanism is proposed to account for the unusual observed trend in dielectric constant.
  • Thumbnail Image
    ItemOpen Access
    High tunable dielectric response of Pb0.87Ba0.1La0.02 (Zr0.6Sn0.33Ti0.07) O3 thin film
    (American Institute of Physics, 2010-08-15T00:00:00Z) Correia, T. M.; Zhang, Qi
    The permittivity maximum of a sol-gel derived Pb0.87Ba0.1La0.02 (Zr0.6Sn0.33Ti0.07) O3 (PBLZST) thin film was observed to appear at Tm=70 ºC rather than at 40 ºC as observed in the bulk ceramics with the same composition. Measurements of permittivity vs. electric field (E) present two maximums at 60 (polarizing) and 25 kVcm-1 (depolarizing), corresponding to antiferroelectric- ferroelectric and ferroelectric-antiferroelectric phase transitions, respectively. Calculations of tunability and Figure-of-Merit (FOM) display a maximum value of 75% at E = 350 kV cm-1 and ~ 141, respectively. These high tunable dielectric responses imply that PBLZST thin films can be an attractive material for tunable device application
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    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
  • Thumbnail Image
    ItemOpen Access
    Thickness-dependent electrocaloric effect in mixed-phase Pb0.87Ba0.1 La0.02 (Zr0.6Sn0.33Ti0.07) O3 thin films
    (The Royal Society, 2016-07-11) Correia, T. M.; Zhang, Qi
    Full-perovskite Pb0.87Ba0.1La0.02(Zr0.6Sn0.33Ti0.07)O3 (PBLZST) thin films were fabricated by a sol–gel method. These revealed both rhombohedral and tetragonal phases, as opposed to the full-tetragonal phase previously reported in ceramics. The fractions of tetragonal and rhombohedral phases are found to be strongly dependent on film thickness. The fraction of tetragonal grains increases with increasing film thickness, as the substrate constraint throughout the film decreases with film thickness. The maximum of the dielectric constant (εm) and the corresponding temperature (Tm) are thickness-dependent and dictated by the fraction of rhombohedral and tetragonal phase, with εm reaching a minimum at 400 nm and Tm shifting to higher temperature with increasing thickness. With the thickness increase, the breakdown field decreases, but field-induced antiferroelectric–ferroelectric (EAFE−FE) and ferroelectric–antiferroelectric (EFE−AFE) switch fields increase. The electrocaloric effect increases with increasing film thickness.