H. Y. Tian

Enhanced ferroelectric and piezoelectric properties in doped lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films

Doping effects with respect to the electrical properties of morphotropic phase boundary (Bi0.5Na0.5)0.94Ba0.06TiO3 thin films epitaxially grown on CaRuO3 electroded (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) substrates were investigated. Substantial enhancement of ferroelectricity and piezoelectricity has been achieved in La+Ce codoped films with a remanent polarization Pr of 29.5 μC/cm2 and a remanent piezoelectric coefficient d33,f of 31 pm/V, whereas Mn doping seems more favorite to reduce the leakage current by two order of magnitude. Both doped films exhibited diodelike I-V characteristics, which are correlated with resistance switching effect.

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

Ba(Zr0.2Ti0.8)O3 (BZT) thin films on Pt(111)∕Ti∕SiO2∕Si(100) substrates without and with CaRuO3 (CRO) buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25–35nm; the average grain size of BZT/CRO films is about 80nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ∼70% and 37 and 75% and 36, respectively, under an applied field of 400kV∕cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed.

Microstructure and dielectric relaxor properties for Ba0.5Sr0.5TiO3/La0.67Sr0.33MnO3 heterostructure

Ferroelectric and magnetoresistance heterostructure (Ba,Sr)TiO3/(La,Sr)MnO3 (BST/LSMO) heterostructure is deposited epitaxially on SrTiO3 (001) substrate by pulse laser deposition. The phase structures of the BST/LSMO heterostructure are characterized by x-ray diffraction. Cross-sectional transmission electron microscope shows a substantial interdiffusision between BST and LSMO layers. The dielectric properties and conductivity of BST/LSMO heterostructure is measured as a function of temperature, frequency, and electric field. The dielectric constant dependence on electric field, e vs E, exhibits a strong nonlinear behavior in the temperature from 20 to 300 K, while e(E=0) vs T relation shows a dielectric relaxor characteristic. Furthermore, the dielectric constant (E=0 kV/cm) and the dielectric tunability (E=200 kV/cm) are found to be similar temperature dependencies. Last, in the temperature regime where a semiconduction-type conduction became dominate, the activation thermal energy of BST/LSMO heterost...

Thickness dependence of in-plane dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 thin films epitaxially grown on LaAlO3

The authors have studied the effects of film thickness on the lattice strain and in-plane dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 thin films epitaxially grown on LaAlO3 (001) single crystal substrates. With increasing film thickness from 20to300nm, the in-plane lattice parameter (a) increased from 0.395to0.402nm while the out-of-plane lattice parameter (c) remained almost unchanged, which led to an increased a∕c ratio (tetragonality) changing from 0.998 to 1.012 and consequently resulted in a shift of Curie temperature from 306to360K associated with an increase of the in-plane remnant polarization and dielectric constant of the film.

Dielectric properties and abnormal C-V characteristics of Ba0.5Sr0.5TiO3–Bi1.5ZnNb1.5O7 composite thin films grown on MgO (001) substrates by pulsed laser deposition

Highly c-axis oriented Ba0.5Sr0.5TiO3-based composite thin films were grown on MgO (001) single-crystal substrates by pulsed laser deposition and the in-plane dielectric properties of the films evaluated. X-ray diffraction characterization revealed a good crystallinity. The dielectric constant and loss were found to be 200 and 0.001–0.007 at room temperature, respectively. The butterfly-shaped C-V characteristic curve evidenced an enhanced in-plane dielectric tunability of >90% in the films at 1MHz under a dc bias field of 0.8MV∕cm. A brief discussion is given on the abnormal C-V curves. Various tunable microwave applications of Ba0.5Sr0.5TiO3–Bi1.5ZnNb1.5O7 composite thin films are expected.

Dielectric properties of (001)-oriented Ba(Zr0.25Ti0.75)o3 thin films prepared by pulsed laser deposition

Ba(Zr 0.25 Ti 0.75 )O 3 (BZT) thin film was deposited on LaAlO 3 (001) single crystal substrate using pulsed laser deposition. The X-ray diffraction examination reveals that the film is highly (001)-oriented with a pure perovskite phase. Fine grains with size of 20–30 nm in diameter were observed in atomic force microscope image. Dielectric properties of the Ba(Zr 0.25 Ti 0.75 )O 3 thin film was characterized in a broad frequency range (1 kHz–10 GHz). Curie temperature of the film was found to be ∼90°C, which is nearly 100°C higher than that of the Ba(Zr 0.25 Ti 0.75 )O 3 bulk ceramics. The relative permittivity of the film exhibits strong dependence of the dc bias field over the whole frequency range. Microwave measurements, performed between 50 MHz–1 GHz, suggest our Ba(Zr 0.25 Ti 0.75 )O 3 thin film is highly tunable (tunability up to 26.1% at 1 GHz under a dc electric field of 13.3 MV/m).