Direct electrocaloric measurement of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 films using scanning thermal microscopy

S. Crossley, T. Usui, B. Nair, S. Kar-Narayan, X. Moya, S. Hirose, A. Ando, N. D. Mathur
2016 Applied Physics Letters  
We show that scanning thermal microscopy (SThM) can measure reversible electrocaloric (EC) effects in <40 μm-thick ceramic films of the relaxor ferroelectric 0.9Pb(Mg 1/3 Nb 2/3 )O 3 -0.1PbTiO 3 , with the substrate present. We recorded roughly the same non-adiabatic temperature change (0.23 K) for a thinner film that was driven harder than a thicker film (31 V μm -1 across 13 μm versus11 V μm -1 across 38 μm), because the thicker film lay relatively closer to the substantially larger
more » ... tially larger adiabatic values that we predicted by thermodynamic analysis of electrical data. Film preparation was compatible with the fabrication of EC multilayer capacitors (MLCs), and therefore our measurement method may be exploited for rapid characterisation of candidate films for cooling applications. Thermal changes arise when ferroelectric phase transitions are driven by changes of electric field ΔE, but these EC effects are limited to a few kelvin in bulk ceramics 1-4 because |ΔE| is limited by breakdown to ~10 V μm -1 . By contrast, ceramic and polymer films of thickness 1 μm show order-of-magnitude larger breakdown fields, resulting in order-of-magnitude larger EC effects (e.g. 12 K with |ΔE| ~ 100 V μm -1 ) 5,6 that are typically evaluated indirectly 7 from variable-temperature measurements of ferroelectric polarization P(E). Direct measurements of a single film are difficult because small active volumes yield small thermal changes, and these must be both driven and measured on short time scales. Both volume and time-scale problems are exacerbated by the unwanted thermal mass of substrates, which are typically present. Here we use non-contact thermometry to directly measure non-adiabatic temperature change ΔT* in single ceramic films on substrates. Predictions of adiabatic temperature change ΔT based on the indirect
doi:10.1063/1.4938758 fatcat:rparq745cjhfbbbfeeghnozqle