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RESEARCH PRODUCT

Temperature and electric field dependence of the permittivity of Ba0.9Sr0.1TiO3 films epitaxially grown on cuprate electrodes

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Abstract Cuprate, high-temperature superconductors and perovskite ferroelectrics have similar crystal structures and chemical constituents and, therefore, it can be advantageous to deposit epitaxial trilayer capacitors with high-Tc electrodes and operate these at room temperature, well above the transition temperature Tc, in order to achieve a high dielectric constant, tunability, and relatively low microwave loss. Epitaxial heterostructures (200 nm)YBa2Cu3O7−δ/(600 nm)Ba0.9Sr0.1TiO3/(200 nm)YBa2Cu3O7−δ and (200 nm)NdBa2Cu3O7−δ/(600 nm)Ba0.9Sr0.1TiO3/(200 nm)NdBa2Cu3O7−δ were laser deposited on (100)LaAlO3 substrates. The relative dielectric permittivity e/e0 of Ba0.9Sr0.1TiO3 was in the range 900–1250 at T=300 K and f=1 MHz, values considerably higher than those for conventional metal electrodes. e(T) had a sharper maximum at a lower temperature (below room temperature) for Ba0.9Sr0.1TiO3 layers with Nd- than with Y-based cuprate electrodes while there was no peak at all up to 350 K when one of the electrodes was ordinary In metal. e was suppressed 4–10 times when ±15 V bias was applied between the high-Tc electrodes (T=300 K, f=1 MHz), the higher value for the Nd cuprate. Losses, tan δ, for the Ba0.9Sr0.1TiO3 film were high compared to bulk values, they were frequency independent ( f=120  Hz–30 MHz) but decreased with increased bias voltage. The permittivity of Ba0.9Sr0.1TiO3 between NdBa2Cu3O7−δ electrodes could be described by the same model at both low and high electric fields.