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Photovoltaic (PV) effects, power-conversion efficiencies, and structures have been systematically measured in (Bi1-xCax)FeO3-δ ceramics for x = 0.05, 0.10, and 0.15. The heterostructures of indium tin oxide (ITO) film/(Bi1-xCax)FeO3-δ ceramics/Au film exhibit significant PV effects under illumination of λ = 405 nm. The maximum power-conversion efficiency in the ITO/(Bi0.90Ca0.10)FeO2.95 (BFO10C)/Au can reach 0.0072%, which is larger than 0.0025% observed in the graphene/polycrystalline BFO/Pt films [Zang et al., Appl. Phys. Lett. 99, 132904 (2011)]. A theoretical model based on optically excited current in the depletion region between ITO film and Ca-doped BFO ceramics is used to describe the I-V characteristic, open-circuit voltage, and short-circuit current density as a function of illumination intensity. This work suggests that the Ca-substitution can reduce the rhombohedral distortion and stabilize the single-phase structure. [ABSTRACT FROM AUTHOR]

The dielectric response and conductivity have been measured in (Bi1-xNdx)FeO3 (x = 0.0 and 0.05) ceramics as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers, B (in temperature units), every lattice constant, a, and extrinsic barriers, B + Δ, every distance, d, is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and step-like dielectric relaxation in the region of 500-800 K. Good qualitative fits of dielectric dispersion and conductivity are obtained with d = 20-30 nm, B = 8400-8700 K (∼0.72-0.75 eV), and Δ = 2500 K (∼0.215 eV). The resistivity plot of scaled ρ" versus ρ' indicates a contribution of grain boundaries or internal defects to the conductivity. [ABSTRACT FROM AUTHOR]

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO-5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic-paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)-orthorhombic (O)-cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO-5%BT exhibits a R-C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO-5%BT remains less than 0.04 below 150 °C. [ABSTRACT FROM AUTHOR]

In situ high-resolution synchrotron x-ray diffraction, dielectric permittivity, hysteresis loop, and polarization current, were used to investigate phase transitions of (211)-cut 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal before and after an electric (E) field poling. A rhombohedral (R)–tetragonal (T)–cubic transition sequence was observed upon zero-field heating in both unpoled and poled samples. Before the R–T transition takes place, an extra dielectric and polarization current anomalies near 365 K were observed in the poled sample due to a transition of polarization ordering. The direct piezoelectric coefficient d33 exhibits a rapid increase for poling at E=1.0–1.3 kV/cm, followed by an overpoling behavior. The increment of polarization ordering plays an important role while the high piezoelectric response builds up. [ABSTRACT FROM AUTHOR]

In situ x-ray diffraction spectra (25-1000 °C) have been measured as a function of temperature for proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 (x=0.0-0.4) ceramics in CO2 atmosphere. Atomic vibrations before and after exposure to CO2 were obtained by using the micro-Raman scattering (150-1600 cm-1). Ba(Zr0.8Y0.2)O2.9 and Ba(Zr0.6Ce0.2Y0.2)O2.9 reveal a promising thermal stability in CO2 without apparent decomposition up to 1000 °C. However, Ba(Zr0.5Ce0.3Y0.2)O2.9 and Ba(Zr0.4Ce0.4Y0.2)O2.9 exhibit thermally stable below 550 °C and then proceed an obvious chemical decomposition of BaCO3 and Zr0.8-xCexY0.2O2 above 550 °C, which were clearly evidenced by the Raman vibrations of 1057 and 466 cm-1, respectively. A first-order orthorhombic-hexagonal structure transition was confirmed in BaCO3 in the region of 810-850 °C upon heating. This study suggests that the Ba(Zr0.8-xCexY0.2)O2.9 ceramics with x¿0.2 are promising candidates for proton-conducting applications in CO2-containing environment. [ABSTRACT FROM AUTHOR]

Phase transformations of (110)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 single crystal before and after an electric (E)-field poling have been investigated by means of dielectric permittivity, polarization current, hysteresis loop, and in situ x-ray diffraction as a function of temperature. An R-T-C transition sequence was observed in the unpoled sample upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. After a prior E-field poling, the crystal underwent an R-O(R)-T-C phase sequence with significant responses in polarization current. O(R) represents that the minor R phase coexists in the orthorhombic matrix. The dielectric permittivities with and without a prior poling were found to follow the Curie–Weiss equation, [variant_greek_epsilon]′=C/(T-T0), above the Burns temperature 505 K with the same constants C=1.43×105 K and T0=462 K. [ABSTRACT FROM AUTHOR]

Phase transformations of (111)-cut Pb(Mg1/3Nb2/3)1-xTixO3 (x=0.30) single crystals before and after an electric (E)–field poling have been investigated by means of dielectric permittivity, hysteresis loop, polarization current, and in situ x-ray diffraction as a function of temperature. An R-T-C transition sequence was observed in the unpoled sample upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. After a prior E-field poling, an extra intermediate monoclinic (possible MA) phase was induced and the crystal underwent an R-MA-T-C phase sequence with significant responses in polarization current. The dielectric dispersion was diminished after poling and reappeared in the cubic state. The dielectric permittivities with and without a prior poling were found to follow the Curie–Weiss equation, [variant_greek_epsilon]′=C/(T-T0), above the Burns temperature 505 K with the same constants C=1.9×105 K and T0=460 K. [ABSTRACT FROM AUTHOR]

This work aims to study thermal stability, frequency response, and refractive indices in a (001)-cut Pb(Zn1/3Nb2/3)0.90Ti0.10O3 (PZNT10%) crystal before and after an electric (E)-field poling, which are important for piezoelectric and optical uses. Dielectric permittivities have been measured as functions of temperature, frequency, and poling strength. The dielectric absorption reveals a broad dipolar relaxation in the region of 260–310 K in the unpoled sample. Piezoelectric resonances were observed in the poled sample and show significant changes while phase transitions are taking place. The unpoled crystal shows almost no birefringence, indicating that the structure averaged over the optically anisotropic ferroelectric domains is optically isotropic. Birefringence appears after an E-field poling and shows a “negative” uniaxial distortion. The Cauchy equations for ordinary no and extraordinary ne refractive indices were determined between 0.45 and 1.4 μm. However, the phase-matching criterion for second harmonic generation was not found. [ABSTRACT FROM AUTHOR]

The Brillouin and Raman scattering from a complex single crystal from the tungsten-bronze family, (K[sub 0.5]Na[sub 0.5])[sub 0.2](Sr[sub 0.75]Ba[sub 0.25])[sub 0.9]Nb[sub 2]O[sub 6] doped with Cu[sup 2+] (KNSBN:Cu), have been comparatively studied in a wide temperature range around the ferroelectric transition. Step-like anomalies in hypersonic velocity and damping confirm the first-order structural transition. These anomalies look like some perturbations on the high-temperature slopes of both a broad dip in sound velocity and a broad maximum in damping that develop in a wide temperature range. The acoustic behavior of KNSBN:Cu does not simply follow the Landau theory prediction valid for many ferroelectrics. Instead it resembles that of relaxors, to which the KNSBN:Cu behavior is analogous intrinsically. The total intensity of the Raman spectra as well as the intensity of separate internal and external vibrations and their width correlate with acoustic anomalies, namely there are step-like drops at the same temperature as the first-order transition and a broad range where the intensity is drastically increased. All these broad anomalies imply the existence of a wide preceding phase in respect to the relaxor ferroelectric state. Unusual properties of this preceding phase are discussed as well as the phase diagram relation to the dynamical evolution of other relaxors from the perovskite family, such as PbMg[sub l/3]Nb[sub 2/3]O[sub 3] and Na[sub l/2]Ba[sub l/2]TiO[sub 3]. [ABSTRACT FROM AUTHOR]

Spontaneous magnetization and photovoltaic (PV) effects have been measured in (Bi1-xBax)FeO3-δ ceramics for x=0.05, 0.10, and 0.15. The substitution of Ba2+ ion in the A site of the perovskite unit cell can effectively enhance the ferromagnetic magnetization. The heterostructure of indium tin oxide (ITO) film/(Bi1-xBax)FeO3-δ ceramic/Au film exhibits significant PV effects under illumination of λ=405 nm. The PV responses decrease with increasing Ba concentration. The maximum power-conversion efficiency in the ITO/(Bi0.95Ba0.5)FeO2.95/Au can reach 0.006%. A theoretical model based on optically excited current in the depletion region between ITO film and (Bi1-xBax)FeO3-δ ceramics is used to describe the I-V characteristic, open-circuit voltage (Voc), and short-circuit current density (Jsc) as a function of light intensity. [ABSTRACT FROM AUTHOR]

Normal piezoelectric coefficient d33, domain structure, and x-ray diffraction of a (001)-cut Pb(In1/2Nb1/2)0.70Ti0.30O3 (PIN-30%PT) single crystal have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Piezoelectric coefficient d33 exhibits a rapid increase at E=1–3 kV/cm and reaches a maximum of about 1200 pC/N near E=6 kV/cm. Structural d spacing and domain structure results suggest that polarization rotation from rhombohedral to monoclinic MA phases causes the high piezoelectric response. Overpoling phenomenon associated with a sudden reduction of d33 with increasing field was not evidenced. [ABSTRACT FROM AUTHOR]

This work presents dielectric resonance in Pb(Mg1/3Nb2/3)1-xTixO3 crystals after electric (E)-field poling, which is crucial for piezoelectric applications. Dielectric permittivity has been measured as functions of temperature, frequency, poling E-field strength, and Ti content (x=25% and 34%). Frequency-dependent dielectric spectroscopy after poling exhibits multiple piezoelectric resonances between 0.2 and 1 MHz, and can be described by the forced-damped-oscillator model. The resonant spectra show significant changes while phase transitions are taking place. [ABSTRACT FROM AUTHOR]

The temperature dependence of the 17O NQR spectra in TlH2PO4 has been measured using a proton-17 O nuclear quadrupole double resonance technique. The results show that the protons in the short one-dimensionally linked O1–H1--O1 and O2–H2--O2 hydrogen bonds are moving between two equilibrium sites above Tc and freeze into one of the off-center sites below Tc. The protons in the asymmetric O3–H3--O4 hydrogen bonds are static and ordered above and below Tc. [ABSTRACT FROM AUTHOR]