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Layered oxide materials having alternating repeated layer thicknesses of 10 nm or less are difficult to make, especially with sharp interfaces. Nanostructured thin films having repeated layers of two different oxide materials were obtained by using pulsed laser deposition and two independent stationary targets consisting of Al 2 O 3 and BaTiO 3 . Desired thicknesses were achieved by using a specific number of pulses from a 248-nm KrF excimer laser, at an energy of 450 mJ / pulse , a galvanometer mirror system, and a background pressure of oxygen. Trends in material properties were identified by systematically varying the number of pulses for multiple nanostructured thin films and comparing the resulting properties measured using in-situ spectroscopic ellipsometry and ex-situ capacitance measurements, including relative permittivity and loss. Four films were deposited with a goal of having 0.25-, 1-, 4-, and 10-nm thick layers, and each ∼ 220 nm thick. Ellipsometry data were modeled in situ to calculate thickness, n and k . A representative transmission electron microscopy measurement was also collected for the 10-nm sample with corresponding x-ray photoelectron spectroscopy and energy disperive x-ray spectroscopy. Ellipsometry and capacitance measurements were all performed on each of the samples, with one sample having calculated impedance greater than 30 GOhm at 0.001 Hz.

The effect of pressure on the crystal structure of HfW2O8 has been investigated by neutron powder diffraction. At a hydrostatic pressure of 0.62 GPa at room temperature the cubic material transforms, with a 5% reduction in volume, to the same orthorhombic phase that is seen in the isostructural compound ZrW2O8 above 0.21 GPa. The transformation is sluggish, requiring about 24 h to complete at constant pressure. Once formed, the orthorhombic phase is retained upon release of pressure. Upon heating to 360 K, the metastable orthorhombic phase transforms back to the cubic phase. The substantially higher pressure for the cubic-to-orthorhombic transition in HfW2O8, compared to ZrW2O8, may be important for the application of this material in composites with controlled thermal expansion because rather large local pressures can occur in such composites.

The crystal structure of ${\mathrm{ZrW}}_{2}{\mathrm{O}}_{8}$ and its variation with pressure and temperature have been investigated by in situ neutron powder diffraction. At room temperature, the cubic \ensuremath{\alpha} phase is stable below 0.21 GPa, where a first-order transition to the orthorhombic \ensuremath{\gamma} phase, accompanied by a 4.95% reduction in volume occurs. The transition involves the inversion of one third of the ${\mathrm{W}}_{2}{\mathrm{O}}_{8}$ units, which is made possible by the migration of oxygen atoms that are bonded to only one W atom in the cubic phase. ${\mathrm{WO}}_{4}$ tetrahedra tilt off the threefold axes of the cubic cell and oxygen atoms that are coordinated to only one W atom in the cubic phase become coordinated to two W atoms in the orthorhombic phase. In spite of its smaller volume, the orthorhombic phase has a volume compressibility $[(\ensuremath{\Delta}V/\ensuremath{\Delta}P)/V=\ensuremath{-}1.53(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}{\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}]$ that is slightly larger than that of the cubic phase $[\ensuremath{-}1.38(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}{\mathrm{GPa}}^{\mathrm{\ensuremath{-}}1}].$ This appears to result from a larger contribution of coordinated tilting of the ${\mathrm{ZrO}}_{6}$ octahedra and ${\mathrm{WO}}_{n}$ polyhedra to the compression. The orthorhombic phase is retained upon release of pressure. Below room temperature, the metastable orthorhombic phase exhibits an average negative volume thermal expansion $[(\ensuremath{\Delta}V/\ensuremath{\Delta}T)/V]$ of $\ensuremath{-}3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{\mathrm{K}}^{\mathrm{\ensuremath{-}}1},$ which is an order of magnitude smaller than that for the cubic phase $(\ensuremath{-}2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{K}}^{\mathrm{\ensuremath{-}}1}),$ apparently because of the reduced framework flexibility of the orthorhombic phase. Above room temperature, the thermal expansion of the orthorhombic phase becomes positive, prior to a first-order transition back to the cubic phase that occurs at about 390 K.

Crystal structures, magnetic and transport properties, and electronic band structures for four compounds with the pyrochlore structure, ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7},$ which exhibits colossal magnetoresistive behavior, and insulating ${A}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7} (A=\mathrm{Y},\mathrm{}\mathrm{In}$ and Lu), are discussed. The cubic unit cell dimensions increase with increasing ionic size of the ${A}^{3+}$ ions. The ferromagnetic behavior is consistent with a superexchange interaction of ${\mathrm{Mn}}^{4+}$ spins with an intermediate Mn-O-Mn bond angle of about $130\ifmmode^\circ\else\textdegree\fi{}.$ In ${\mathrm{In}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7},$ strong hybridization of the $\mathrm{In}(5s)/\mathrm{Tl}(6s)$ orbital with $\mathrm{O}(2p)$ and $\mathrm{Mn}(3d)$ may enhance the ferromagnetic interaction, leading to high transition temperatures over 120 K. The metallic behavior of ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ also originates from the hybridization among $\mathrm{Tl}(6s), \mathrm{O}(2p),$ and $\mathrm{Mn}(3d).$ The free-electron-like minority down-spin band crosses the Fermi energy, leading to spin-polarized conduction. At the ferromagnetic Curie temperature, where majority local spins align, spin-polarized conduction electrons are produced: Thus, a ferromagnetic-and-metallic state appears in the ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ pyrochlore.

The pressure effect on the magnetic and crystallographic structures of the materials UCu 2 Ge 2 , and U(Ni 0.05 Cu 0.95 ) 2 Ge 2 are studied by neutron diffraction in the applied pressure range of ambient to 0.63 GPa, at room temperature and 60 K. The compressibilities of the materials are found to be isotropic, and very similar for both materials and temperatures. This isotropy is explained by a free-electron gas control of the compressibility. No pressure effect on the magnetic structures or on the magnitude of the magnetic moments was observed for both materials. This result is discussed in the framework of the RKKY model.

It has been challenging to achieve combined strong magnetoelectric coupling and narrow ferromagnetic resonance (FMR) linewidth in multiferroic heterostructures. Electric field induced large effective field of 175 Oe and narrow FMR linewidth of 40 Oe were observed in FeCoSiB/Si/SiO2/PMN-PT heterostructures with substrate clamping effect minimized through removing the Si substrate. As a comparison, FeCoSiB/PMN-PT heterostructures with FeCoSiB film directly deposited on PMN-PT showed a comparable voltage induced effective magnetic field but a significantly larger FMR linewidth of 283 Oe. These multiferroic heterostructures exhibiting combined giant magnetoelectric coupling and narrow ferromagnetic resonance linewidth offer great opportunities for integrated voltage tunable RF magnetic devices.

Fe27.45Co30.19B42.36 (referred to as FeCoB) films with 100 nm in thickness were co-sputtered on (011)-cut lead zinc niobate-lead titanate (PZN-PT) single crystal substrate under RF powers of 80 W for Fe50Co50 target and 120 W for B target, respectively. The anisotropy field HK of the FeCoB/PZN-PT multiferroic composite is increased by more than 10 times, from 56 to 663 Oe under the E-field from 0 to 7 kV/cm due to the strong magnetoelectric coupling, corresponding to a large tunability of HK of 86.7 Oe cm/kV. At the same time, the self-bias ferromagnetic resonance frequency fFMR is dramatically shifted upwards by an electric field from 2.57 to 9.02 GHz with an increment of 6.45 GHz, corresponding to E-field tunablity of fFMR 921.4 MHz.cm/kV. These features demonstrate that FeCoB/PZN-PT multiferroic laminates prepared under an integrated circuits process are promising in fabrication of E-field tunable monolithic microwave integrated circuits (MMIC) devices and their components.

We report strong voltage tuning of magnetism in FeGaB deposited on [011]-poled Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ternary single crystals to achieve more than 2 times broader operational range and increased thermal stability as compared to heterostructures based on binary relaxors. Voltage-induced effective ferromagnetic resonance field shift of 180 Oe for electric field from −6.7 kV/cm to 11 kV/cm was observed in FeGaB/PIN-PMN-PT heterostructures. This strong magnetoelectric coupling combined with excellent electric and temperature stability makes FeGaB/PIN-PMN-PT heterostructures potential candidates for high-power tunable radio frequency/microwave magnetic device applications.

In situ neutron powder diffraction has been used to show that the application of hydrostatic pressure at room temperature produces a transformation of ZrW 2 O 8 from the cubic to an orthorhombic phase beginning at 2.1 kbar and completed by 3.1 kbar, with a 5% reduction in volume. After release of pressure, the orthorhombic phase is retained at room temperature. Its thermal expansion is negative below room temperature, but is positive above room temperature with a transformation back to the cubic phase at about 390 K. The WO 4 groups are found to play the dominant role in both phase transformations. The volume compressibilities of the cubic and orthorhombic phases are 1.38 × 10 −3 and 1.53 × 10 −3 kbar −1 , respectively.

The structures of R2Fe17−xAlxC1 (R = Y, Pr, Tb, Ho, Er; x = 2, 4) have been studied with neutron diffraction. All of the compounds have the rhombohedral Th2Zn17 structure (space group R-3m) except for the Er series which has the disordered hexagonal Th2Ni17 structure (space group P 63/mmc). Both substitution of Fe and interstitial C can trigger the structure change from hexagonal to rhombohedral in the heavy rare-earth 2 : 17 compounds. In the rhombohedral compounds, Al is found to prefer the 18th site and fills up the 6c site more rapidly at higher Al concentration. No Al is found at the 9d site. C is mainly found at the 9e site. In the Pr compounds, a small amount of C is also found at the 18g site. In the Er samples, al is found at the Fe 6g site which is the equivalent of the 9d site in the rhombohedral structure.

The energy storage properties of antiferroelectric (AFE) Pb0.96La0.04Zr0.98Ti0.02O3 (PLZT 4/98/2) thin films were investigated as a function of temperature and applied electric field. The results indicated that recoverable energy density (Ure) and charge-discharge efficiency (η) of PLZT (4/98/2) depend weakly on temperature (from room temperature to 225 °C), while Ure increases linearly and η decreases exponentially with increasing electric field at room temperature. These findings are explained qualitatively on the basis of the kinetics of the temperature-induced transition of AFE-to-paraelectric phase and the field-induced transition of AFE-to-ferroelectric phase, respectively. The high Ure (≈61 J/cm3) and low leakage current density (≈3.5 × 10−8 and 3.5 × 10−5 A/cm2 at 25 and 225 °C, respectively) indicate that antiferroelectric PLZT (4/98/2) is a promising material for high-power energy storage.

In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW 2 O 8 ) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin. The relative thermal expansion and compressibilities of the cubic and orthorhombic forms can be explained in terms of the “cross-bracing” between polyhedra that occurs as a result of the phase transition.

Ceramic thin films with high dielectric constant and high breakdown strength hold special promise for advanced electronics applications. We deposited lanthanum-doped lead zirconate titanate (PLZT) on base metal foils (film-on-foils) by chemical solution deposition. The PLZT film-on-foils were characterized over a wide temperature range between room temperature and 200°C. For ≈2-μm-thick PLZT films grown on LaNO3-buffered nickel foils at room temperature, we measured a dielectric constant of ≈1300, dielectric loss of ≈0.07, remanent polarization of ≈26 μC/cm2, coercive field of ≈29 kV/cm, leakage current density of ≈9.2 × 10−9 A/cm2, and energy density of ≈67 J/cm3. Dielectric breakdown strength was determined to be ≈2.6 × 106 V/cm by Weibull analysis. These and other results reported here indicate that electronic devices with film-on-foil capacitors would possess higher performance, improved reliability, and enhanced volumetric and gravimetric efficiencies compared with traditional dielectric capacitors.

Rayleigh analysis has been used to investigate the temperature dependence of the dielectric response of relaxor ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 films grown on platinized silicon substrates by chemical solution deposition. The irreversible contribution to dielectric permittivity maximizes at 50 °C and decreases with further temperature increase; while the intrinsic/reversible contribution is weakly dependent on temperature. The relaxor ferroelectric transition temperature Tm increases from 160 °C to 172 °C when the frequency increases from 1 kHz to 100 kHz. The dielectric nonlinearity decreases with temperature: falling from 0.012 cm/kV at room temperature to 0.005 cm/kV at 225 °C in tests at 1 kHz.

This paper reports the bipolar resistive switching (RS) effect of the Nd0.05Bi0.95FeO3/Nb:SrTiO3 heterostructure fabricated by pulsed laser deposition. This heterostructure shows a high RS ratio of over 600 at a read voltage of −0.3V after applying 5V/−8V pulse voltages. Moreover, the resistance states could be switched reversibly among multilevel resistance states by changing the magnitude of set or reset pulse voltages, which shows promise for multilevel nonvolatile memory application. The mechanism of the RS between high- and low-resistance states could be attributed to the carrier injection-trapped/detrapped process, which changes the height and thickness of the barrier at the Nd0.05Bi0.95FeO3/Nb:SrTiO3interface.

The dielectric properties of lead lanthanum zirconate titanate (PLZT) thin films on platinized silicon (Pt/Si) with and without ZrO2 insertion layers were investigated in the temperature range from 20 °C to 300 °C. Permittivity, dielectric loss tangent, and tunability were reduced for the samples with ZrO2 insertion layers compared to those without the layers. Additionally, the permittivity was less dependent on frequency over the broad temperature range studied (20–300 °C). The leakage current behavior of the PLZT films with and without ZrO2 insertion layers was also investigated, and on the basis of those results, a probable conduction mechanism has been suggested. The improved electrical properties in the PLZT with ZrO2 layers are attributed to the ZrO2 layer blocking the mobile ionic defects and reducing free charge carriers to transport.

We deposited ferroelectric (Pb0.92La0.08)(Zr0.52Ti0.48)O3 films of ≈0.35 to ≈3.1 μm in thickness on platinized silicon substrates by chemical solution deposition. A dielectric constant of ≈1350 and dielectric loss of ≈0.04 were measured at room temperature. Hysteresis loop tests revealed that the remanent polarization increases while the coercive field decreases with PLZT film thickness. The residual stress in the PLZT films, as determined by the x-ray diffraction sin2ψ method, decreased from ≈380 to ≈200 MPa when the film thickness increased from 0.35 to 3.1 μm. The dependence of the residual stress (σ) on the PLZT film thickness (t) can be described by an empirical equation, σ = A0exp(−t2/λ2), with A0 ≈ 390 MPa and λ ≈ 3.8 μm.

We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface.

Ferroelectric Pb0.92La0.08Zr0.52Ti0.48Oδ films (≈2-μm thickness) were grown on LaNiO3-buffered nickel foils by chemical solution deposition. Their ferroelectric and dielectric properties were measured as a function of temperature. With increasing temperature from room temperature to 200 °C, back-switching polarization increased while spontaneous polarization, remanent polarization, and coercive field decreased. The domain wall energy barrier was determined from the temperature-dependent back-switching polarization. Decreased irreversible/extrinsic and reversible/intrinsic dielectric responses were observed with increasing frequency. The ratio of irreversible to reversible contributions to dielectric nonlinearity was analyzed by the Rayleigh law. This ratio decreased with increasing frequency from 500 Hz to 500 kHz.

A series of TiO2 nanocomposite photoanodes with different amounts of Ag nanowire (AgNW) coated with SiO2 in a AgNW@SiO2 core–shell structure are prepared by a ball milling method and applied to assemble a series of dye-sensitized solar cells (DSSCs). The influence of AgNW@SiO2 on the performance of the TiO2–AgNW photoanodes and DSSCs is investigated. Studies indicates that the range and strength of light absorption of the TiO2 photoanodes, the photon capture ability of the dye molecules, and the short-circuit current density (Jsc) are significantly increased while the dark current is decreased due to the incorporation of AgNW@SiO2. The optimal properties are obtained in a DSSC with a Jsc of 11.83 mA cm−2, and an overall photoelectric conversion efficiency (η) of 6.26%, significantly superior to those of the DSSC with a pure TiO2 photoanode. The enhancements of Jsc and η are attributed to the increase of light coupling and thus the light absorption of the dye due to the localized surface plasmon resonance and the possible enhanced light scattering of AgNW@SiO2 in the photoanode.

This paper reports the resistive switching effects of ZnO, CeO2 and CeO2/ZnO stacked heterostructure deposited on Nb:SrTiO3 substrates by pulsed laser deposition. The CeO2/ZnO stacked heterostructure shows high resistive switching ratio of over 104 at a read voltage of −0.5 V and an expected retention ability of ten years, which is better than that of ZnO- or CeO2-based device. Furthermore, multilevel resistance states could be adjusted by changing the maximum value of the applied voltage, which shows promise for high-performance nonvolatile multilevel memory application. Studies indicated that the trap-mediated space charge limited conduction governs the low- and high-resistance states. The good resistive switching characteristics of CeO2/ZnO stacked heterostructure could be attributed to the carrier injection-trapped/detrapped process at the CeO2/ZnO interface and ZnO films in which oxygen vacancies act as ‘trapping center’.

Hard piezoelectric ceramics of manganese (Mn)-modified 0.36BiScO3–0.64PbTiO3 (0.36BS–0.64PTM) with a high Curie temperature were prepared using the traditional solid-state reaction method. The effects of different concentrations of Mn on the structure, dielectric and piezoelectric properties of the 0.36BS–0.64PTM ceramics were investigated. X-ray diffraction results indicated that the 0.36BS–0.64PTM ceramics showed a single perovskite structure with tetragonal symmetry and the c/a ratio decreased slightly with increasing Mn content. The grain sizes of the 0.36BS–0.64PTM ceramics were enlarged by Mn addition, and their distributions were uniform. The dielectric loss tan δ decreased clearly with the increase in Mn content, and the mechanical quality factor Q m and vibration velocity v 0 were improved significantly at the same time. The Curie temperature T c, the planar electromechanical coupling factor k p, dielectric loss tan δ, mechanical quality factor Q m and vibration velocity v 0 of the 0.36BS–0.64PTM ceramics with 3 mol% Mn were about 431 °C, 0.57, 0.007, 134 and 1.05 m s−1, respectively. The maximum vibration velocity v 0 of the 0.36BS–0.64PTM ceramics is much superior to those of PZT (0.4 m s−1) ceramics and PZT–PZM (0.72 m s−1). These results indicated that the 0.36BS–0.64PTM ceramics are promising candidates for high-temperature and high-power piezoelectric applications.

A TiO2 thin film was deposited on a Nb : SrTiO3 substrate by pulsed laser deposition to form an Ag/TiO2/Nb : SrTiO3/In device. The bipolar resistive switching (RS) effect of this device was investigated. The current–voltage characteristics exhibited pronounced and stable bipolar RS features. The device could be switched to a low resistance state (LRS) at forward voltage and returned to a high resistance state (HRS) at reverse voltage, and the RS ratio R HRS/R LRS reached up to 2 × 103 at a read voltage of −0.5 V. Moreover, the RS ratio could be adjusted by changing the maximum value of the forward or reverse voltage, which shows promise for multilevel memories. These results are discussed by considering carrier injection-trapped/detrapped process of the heterostructure and show high potential for nonvolatile memory applications.

We report the epitaxial growth of multiferroic BiFeO3 (BFO) film on Si(001) substrate by pulsed laser deposition using CeO2/yttria-stabilized zirconia (YSZ) as buffer layers. The epitaxial relationships of the films were BFO(001)/CeO2(001)/YSZ(001)/Si(001) for out-of-plane and [110]BFO‖[100]CeO2‖[100]YSZ‖[100]Si for in-plane, respectively. Capacitance-voltage characteristics of a Pt/BFO/CeO2/YSZ/p-Si capacitor exhibited clockwise hysteresis loops with a large memory window of 2.5 V at sweeping voltages of ±16 V. Both the high and low capacitance values showed no obvious degradation after 104 s. The improved retention property was attributed to the use of high-k CeO2/YSZ insulating layers that effectively eliminated the charge trapping in the heterostructure.

Piezoelectric ceramic (1 − x)Bi(Sc3/4In1/4)O3-xPbTiO3 (BSIPT) (0.45 ≤ x ≤ 0.70) solid solutions near the morphotropic phase boundary (MPB) were developed for high temperature piezoelectric transducer and actuator applications. It was found that the MPB composition of BSIPT ceramics was in the vicinity of x = 0.6, where it had relatively small tolerance factor t = 0.901 resulting in a high TC of 457 °C, and also optimal properties such as the high Pr = 25.4 μC/cm2, ɛr = 1153, d33 = 201 pC/N, kp = 0.34, and the low Ec = 23.5 kV/cm. Measurements also showed that the depoling temperature was 360 °C, about 200 °C higher than that of commercialized PZT ceramics, which indicated good temperature stability. BSIPT ceramics are promising candidates for high temperature applications.

Pure BiFeO3 (BFO), Nd-doped BFO (BNF) and Nd and Mo co-doped BFO (BNFM) multiferroic thin films were prepared by pulsed laser deposition on Pt/Ti/SiO2/Si substrates. Among these films, the BNFM film exhibited the lowest dielectric loss and leakage current density, a well-saturated P–E loop, excellent charge-retaining ability and fatigue-free behaviour. Furthermore, improved ferromagnetism was observed in this film with a saturation magnetization of ~15 emu cm−3. These significant improvements in ferroelectric and ferromagnetic properties could be preliminarily attributed to the elimination of oxygen vacancies and the increase in the Fe2+ ions in the film by Nd and high-valence Mo co-doping, respectively.

High-valence Pr-doped BiFeO3 (BPF) multiferroic thin film was prepared by pulsed laser deposition on a Pt∕TiO2∕SiO2∕Si substrate. X-ray diffraction analysis indicates that the BPF film is of pure phase with a polycrystalline perovskite structure. The BPF film exhibited enhanced multiferroic properties: (i) a rectangular-shaped electric hysteresis loop with a large Pr of 75μC∕cm2 and a low Ec of 250kV∕cm at Emax ∼620kV∕cm, (ii) a saturated magnetic hysteresis loop with a large Ms of 58emu∕cm3, and (iii) a fatigue-free behavior after being subjected to 1.2×109 switching cycles, which were superior to, in some aspects, those of La- or Nd-doped BiFeO3 films reported before.