R. K. Zheng

Remanent-polarization-induced enhancement of photoluminescence in Pr3+-doped lead-free ferroelectric (Bi0.5Na0.5)TiO3 ceramic

We found that ferroelectric remanent polarization can remarkably enhance the photoluminescence intensity of Pr3+-doped lead-free (Bi0.5Na0.5)TiO3 ceramics. An enhancement in photoluminescence intensity of ∼35% was obtained in the 0.5u2009mol. % Pr3+-doped sample, attributed to the decrease of crystal symmetry that occurs in poled ferroelectric ceramics. Our results reveal the great potential to enhance the photoluminescence intensity in rare-earth doped ferroelectric ceramics through ferroelectric polarization and to monitor the ferroelectric remanent polarization strength through measuring the photoluminescence spectra. We also found that the threshold of Pr3+ concentration quenching increased in the poled Pr3+-doped lead-free (Bi0.5Na0.5)TiO3 ceramic sample.

Enhanced dielectric properties of highly (100)-oriented Ba(Zr,Ti)O3 thin films grown on La0.7Sr0.3MnO3 bottom layer

Barium zirconate titanate Ba(Zr0.2Ti0.8)O3 (BZT) thin films on La0.7Sr0.3MnO3 (LSMO)-coated Si and Pt∕Ti∕SiO2∕Si substrates have been prepared by pulsed laser deposition and crystallized in situ at 650°C. Four capacitor types of LSMO∕BZT∕LSMO∕Si, Pt∕BZT∕LSMO∕Si, Pt∕BZT∕Pt∕Si, and Pt∕BZT∕LSMO∕Pt∕Si were prepared to investigate the structural and dielectric properties, tunability, and figure of merits. Among them, the high (100)-oriented BZT films were grown on the (100)-textured LSMO and (111)-textured Pt electrodes. The results show that the LSMO∕BZT∕LSMO∕Si has the highest dielectric constant of 555 and Pt∕BZT∕LSMO∕Pt∕Si has the highest tunability of 73% at 1MHz. The high dielectric constant and tunability have been attributed to the (100) texture of the LSMO bottom layer leading to the decrease of the thickness of the interface of the dead layer.

Effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6−xCaxTiO3 (0⩽x⩽0.3) perovskites

The effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6−xCaxTiO3 (0⩽x⩽0.3) has been studied. Powder x-ray diffraction revealed that the cubic lattice constant a decreases linearly with increasing x from 0 to 0.15, while showing an anomalous expansion between x=0.15 and x=0.18. This, together with the anomalies in the dielectric constants, Curie temperature TC, and elastic constants observed for 0.15 0.15, TC increases persistently up to x=0.25 and thereafter shows a decrease. These variations of TC with x have been interpreted in terms of Ca-doping-induced A-site cation size variance, a substitution of a small amount of Ca ions for Ti ions, and structural phase separation. Upon cooling the longitudinal elastic constant CL shows drastic sof...

Dielectric properties of (100)-oriented Ba(Zr, Ti)O3/La0.7Ca0.3MnO3 heterostructure thin films prepared by pulsed laser deposition

Highly (100)-oriented Ba(Zr0.2Ti0.8)O3/La0.7Ca0.3MnO3 (BZT/LCMO) heterostructure thin films have been grown on Si(100) and Pt(111)/Ti/SiO2/Si(100) substrates prepared by pulsed laser deposition. The structure and surface morphology of the films have been characterized by x-ray diffraction and atomic force microscopy. The dielectric constant of the films changes significantly with applied dc bias field and the films have high tuneability of 59.1%, 52% and 59.4% at an applied field of 400 kV cm−1, respectively, for the BZT film on Pt/Ti/SiO2/Si and the BZT/LCMO heterostructure films on Si and Pt/Ti/SiO2/Si substrates. The tuneability of the BZT/LCMO thin films on Pt-coated Si substrate was higher than that of the BZT thin films on Pt/Ti/SiO2/Si and LCMO/Si substrates. The high tuneability has been attributed to the (100) texture of the films and larger grain sizes. The BZT thin film is an attractive candidate for tuneable microwave device applications.

Microstructure and enhanced in-plane ferroelectricity of Ba0.7Sr0.3TiO3 thin films grown on MgAl2O4 (001) single-crystal substrate

The microstructure and in-plane dielectric and ferroelectric properties of highly oriented Ba0.7Sr0.3TiO3 (BST) thin film grown on MgAl2O4 (001) single-crystal substrate through pulsed laser deposition were investigated. X-ray diffraction measurements indicated that BST had a distorted lattice with a tetragonality a∕c=1.012. The cross-sectional observation under transmission electron microscope revealed that, while most of BST grains grew epitaxially on MgAl2O4, the film also contained a noticeable amount of misoriented grains and dislocations. The electrical measurements indicated that the film had a shifted Curie temperature (TC=78°C) and an enhanced in-plane ferroelectricity (remnant polarization Pr=7.1μC∕cm2) when compared with BST ceramic (TC≈33°C and Pr≈0).

Effects of ferroelectric-poling-induced strain on magnetic and transport properties of La0.67Ba0.33MnO3 thin films grown on (111)-oriented ferroelectric substrates

La0.67Ba0.33MnO3 thin films were epitaxially grown on (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 ferroelectric single-crystal substrates. During ferroelectric poling and polarization rotation, the resistance of La0.67Ba0.33MnO3 films tracks the electric-field-induced in-plane strain of substrates effectively, implying strain-mediated coupling. Upon poling along the [111] direction, ferromagnetism is suppressed for Tu2009 u2009175u2009K, which is explained by magnetoelastic coupling that modifies the films magnetic anisotropy. Our findings also show that the magnetic field has an opposite effect on the strain-tunability of resistance [i.e.,(ΔR/R)strain] above and below the Curie temperature TC, which is interpreted within the framework of phase separation.

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.

Abnormal phase transitions for tetragonal (1−x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 single crystals at low temperature

Dielectric spectroscopy and ultrasonic sound velocity were investigated for tetragonal PMN-xPT single crystals over a wide range of temperature. In addition to the expected phase transition from the tetragonal ferroelectric phase to the cubic paraelectric phase at a high temperature, an abnormal ferroelectric phase transition below room temperature is observed. The low-temperature phase transition shows a relaxor behavior though tetragonal PMN-xPT single crystal is considered to be typical normal ferroelectrics. By comparing the dielectric constants of poled and depoled conditions and by analyzing [BO6] oxygen-octahedra units of perovskite structure, it is suggested that the low-temperature phase transition in poled tetragonal PMN-xPT single crystal could be tetragonal to rhombohedral ferroelectric phase transition.

Coupling of magnetic field and lattice strain and its impact on electronic phase separation in La0.335Pr0.335Ca0.33MnO3/ferroelectric crystal heterostructures

Phase-separated La0.335Pr0.335Ca0.33MnO3 films were epitaxially grown on (001)- and (111)-oriented ferroelectric single-crystal substrates. Upon poling along the [001] or [111] direction, dramatic decrease in resistance, up to 99.98%, and complete melting of the charge-ordered phase were observed, caused by poling-induced strain rather than accumulation of electrostatic charge at interface. Such poling-induced strain effects can be effectively tuned by a magnetic field and mediated by electronic phase separation. In particular, our findings show that the evolution of the strength of electronic phase separation against temperature and magnetic field can be determined by measuring the strain-tunability of resistance [(ΔR/R)strain] under magnetic fields.

Coaction and competition between the ferroelectric field effect and the strain effect in Pr0.5Ca0.5MnO3 film/0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystal heterostructures

The coaction and competition between the ferroelectric field effect and the strain effect in Pr0.5Ca0.5MnO3 (PCMO) film/0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystal heterostructures were studied. Based on different types of resistance-electric field hysteresis loops at various temperatures, it is clearly identified that the strain effect dominates over the ferroelectric field effect for temperature T above the charge-ordering temperature TCO of PCMO. With the strong localization of charge carriers for T < TCO, the ferroelectric field effect strongly competes with the strain effect and finally dominates over the latter for T < 0.8TCO. Moreover, the poling-induced strain effect is considerably enhanced by a magnetic field, demonstrating the important role of the phase separation in understanding the strain effect in such heterostructures.The coaction and competition between the ferroelectric field effect and the strain effect in Pr0.5Ca0.5MnO3 (PCMO) film/0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystal heterostructures were studied. Based on different types of resistance-electric field hysteresis loops at various temperatures, it is clearly identified that the strain effect dominates over the ferroelectric field effect for temperature T above the charge-ordering temperature TCO of PCMO. With the strong localization of charge carriers for T < TCO, the ferroelectric field effect strongly competes with the strain effect and finally dominates over the latter for T < 0.8TCO. Moreover, the poling-induced strain effect is considerably enhanced by a magnetic field, demonstrating the important role of the phase separation in understanding the strain effect in such heterostructures.