Search

In the present work, we have demonstrated a highly sensitive H2 gas sensor using a lanthanum doped ZnO (La_ZnO) thin film operated at 300 °C. Also, a p-type to n-type carrier reversal activity is revealed in the presence of H2 gas species, which predominantly depends on the operating temperature and doping concentration of lanthanum. Pure and La_ZnO (1–10 at. %) thin films were successfully synthesized using a sol-gel route, where a 5 at. % lanthanum doped ZnO thin film shows an outstanding H2 gas sensitivity (400%) among all other samples with an optimized temperature of 300 °C. Moreover, this sensor actively responds to a wide H2 gas concentration (10–500 ppm) with a sensitivity of 0.9 (∼n). Additionally, H2 gas sensing selectivity and mixed gas sensing performance were investigated in the presence of CO and CO2 gas species at optimized temperature (300 °C). Results show that the pure and 1–3 at. % La_ZnO thin films exhibited n-type H2 gas sensing, while p-type sensing behavior was observed for 5% and 10% La_ZnO thin films at 300 °C. It is further observed that O− species are extremely active to CO gas species operating at a high operating temperature (>250 °C). Therefore, despite the emerging p-type behavior of the sensor, the ejected electrons are expected to dominantly reduce the sensor resistance in the presence of CO gas species at 350 °C. The improvement of H2 sensing is further interrelated with the defect levels using Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We report on the thermoelectric properties of strained, highly-oriented, lightly-doped La1–xSrxCoO3 thin films, grown on MgO (100) substrates by pulsed laser deposition. The large lattice mismatch (∼9%), along with the different thermal expansion coefficients, between La1–xSrxCoO3 and MgO, result in the incoherent growth of thin films and the generation of a tensile thermal strain (∼1%). Room temperature resistivity values of the films are similar to those of bulk samples, while the temperature dependence of resistivity of the films does not seem to be affected by the thermal strain. The Seebeck coefficient values of all investigated films are positive but lower than those of their bulk counterparts, throughout the measured temperature range. The lower values of the films' Seebeck coefficient are attributed to the stabilization of mixed Co spin state configuration, which is induced by the thermal strain. As a result of the reduced Seebeck coefficient values, the thermoelectric power factor is suppressed, suggesting that the tensile thermal strain does not favor the thermoelectric behavior of the La1–xSrxCoO3. [ABSTRACT FROM AUTHOR]

LaSb2 has a layered crystal structure along the c-axis with ∼2% difference between the in-plane orthorombic a and b axes. Here, we report on the thermal conductivity, electrical resistivity, and Seebeck coefficient from 10 to 300 K as well as the magnetoresistance at 10 K. Using the van der Pauw technique on single crystal samples, the in-plane electrical resistivity tensor has been measured and it is found to be isotropic. An anisotropic crystal structure may have isotropic properties, but in the present case, the isotropic nature stems from crystal imperfection. Single crystal X-ray diffraction provides evidence of a mixing of the in-plane a- and b-directions leading to observed diffraction intensity where systematic absences are expected. Whether the underlying structural mechanism is twinning or stacking faults is unknown, but it could be the origin of the previously observed charge density wave states, and it may also explain the high unsaturating linear magnetoresistance reported here. At ambient conditions, LaSb2 is found to be stable in air, with no sign of bulk degradation after 5 years of storage; however, some change is observed in the amorphous background scattering. [ABSTRACT FROM AUTHOR]

We systematically investigate the thermoelectric properties of lanthanum phosphide (LaP) using first-principles calculations together with the Boltzmann transport theory. The dynamic stability of LaP is confirmed based on phonon dispersion. The different atomic masses of La and P atoms lead to an acoustic-optical bandgap that prohibits scattering between acoustic and optical phonon modes. The lattice thermal conductivity κ l is 3.19 W/mK at room temperature, which is less than that of LaAs because of the smaller group velocities and the larger Grüneisen parameter. The calculated phonon-mode contribution to κ l , scattering rate, and mean free path may provide significant guidance to further theoretical and experimental research. The power factor reaches 0.012 W m−1 K−2 at a carrier concentration of 1.05 × 10 20 c m − 3 , which is comparable to the power factor of the typical thermoelectric material Bi2Te3. This reasonable power factor and thermal conductivity suggest that LaP is a promising thermoelectric material. The dependence of the figure of merit ZT on carrier concentration n and temperature T indicates that a high ZT can be obtained by increasing the temperature and tuning the carrier concentration. [ABSTRACT FROM AUTHOR]

LaSb2 has a layered crystal structure along the c-axis with ∼2% difference between the in-plane orthorombic a and b axes. Here, we report on the thermal conductivity, electrical resistivity, and Seebeck coefficient from 10 to 300 K as well as the magnetoresistance at 10 K. Using the van der Pauw technique on single crystal samples, the in-plane electrical resistivity tensor has been measured and it is found to be isotropic. An anisotropic crystal structure may have isotropic properties, but in the present case, the isotropic nature stems from crystal imperfection. Single crystal X-ray diffraction provides evidence of a mixing of the in-plane a- and b-directions leading to observed diffraction intensity where systematic absences are expected. Whether the underlying structural mechanism is twinning or stacking faults is unknown, but it could be the origin of the previously observed charge density wave states, and it may also explain the high unsaturating linear magnetoresistance reported here. At ambient conditions, LaSb2 is found to be stable in air, with no sign of bulk degradation after 5 years of storage; however, some change is observed in the amorphous background scattering. [ABSTRACT FROM AUTHOR]

Rotations and distortions of oxygen octahedra in perovskites play a key role in determining their functional properties. Here, we investigate how octahedral rotations can couple from one material to another in La2/3Sr1/3MnO3/SrTiO3 epitaxial heterostructures by first principles density functional theory calculations, emphasizing the important differences between systems oriented perpendicular to the (111)- and (001)-facets. We find that the coupling length of out-of-phase octahedral rotations is independent of the crystalline facet, pointing toward a steric effect. However, the detailed octahedral structure across the interface is significantly different between the (111)- and (001)-orientations. For (001)-oriented interfaces, there is a clear difference whether the rotation axis in SrTiO3 is parallel or perpendicular to the interface plane, while for the (111)-interface, the different rotations' axes in SrTiO3 are symmetry equivalent. Finally, we show that octahedral coupling across the interface can be used to control the spatial distribution of the spin density. [ABSTRACT FROM AUTHOR]

We have investigated the electrical and dielectric properties of rare earth perovskites-type oxide (LaErO3 and LaHoO3) by using impedance spectroscopy, respectively, over a frequency and temperature range of [0.6 kHz–8MHz] and [673–973 K]. Both oxides crystallize in the orthorhombic structure but exhibit difference in lattice distortions. A correlation between structural properties and dielectric anisotropies is carried out. The analysis of Nyquist semicircles confirms the presence of bulk effects and non-Debye relaxation processes for both compounds. The activation energy, calculated using relaxation time and direct current conductivity models, was found to follow the Arrhenius law. The frequency dependence of alternative current conductivity is described by Jonscher’s universal power law and shows that the conduction mechanism follows the non-overlapping small polaron tunneling model. The investigation of dielectric properties revealed that at low frequencies the dielectric constant was higher for LaHoO3 oxide than that for LaErO3. Modulus formalism examination demonstrates that the relaxation process of studied materials takes place via the hopping mechanism. [ABSTRACT FROM AUTHOR]

A significant structural modification and enhancement of the electrical and magnetic properties with dilute substitution of Zr (≤1mol.%) in the Bi0.8La0.2Fe1-xZrxO3 system has been reported. A mixture of rhombohedral and orthorhombic phases was detected in these conventionally sintered ceramics. Transition from a leaky state to an insulating state was observed upon Zr substitution. This is the first time that a drop in the electrical conductivity as large as 6 orders of magnitude for doping as small as 0.25mol. % in bismuth ferrite systems has been reported. An investigation on the nature of this abrupt transition revealed the dominant role of defects. A proper consideration of possible defect reactions taking place during and after sintering satisfactorily accounts for the observed modulation in the electrical properties. Both AC and DC measurements indicate that, before Zr substitution, ptype hopping conduction prevails with an activation energy as low as ~0.57 eV, whereas the Zr substitution makes oxide ion migration the central mechanism for conduction with the activation energy of ~0.96-1.08 eV. In contrast to that, the magnetic properties of the compounds experience a more subtle effect; a gradual modification of saturation magnetization and coercivity with Zr substitution is observed. Curve fitting of the magnetic hysteresis loops not only allowed extraction of three separate contributions from the magnetic response but also helped to explain the effects of Zr on the magnetic properties. Modifications of structural characteristics and magnetic anisotropy of the samples are believed to be the primary driving force behind the improvement in the magnetic properties. [ABSTRACT FROM AUTHOR]

The systematic study on structural properties of Ba-substituted La0.9Sr0.1Al0.9Mg0.1O3-δ and its correlation with conductivity was carried out. X-ray diffraction patterns indicated that the system formed a single phase composition up to 3% of Ba double substitution at the La-site. Energy dispersive X-ray spectroscopy and XPS results confirmed elemental compositions and revealed the maximum deficiency in oxygen for the 3% Ba-substituted sample. Dense grain formation is observed in SEM images, complementing higher density of these samples (>93%). Electrical conductivity was found to be in correlation with a new structural parameter of the critical triangle of (La/Sr/Ba)- Al/Mg-(La/Sr/Ba). The value of conductivity increased by an order of 2 in a substituted sample as compared to pure LaAlO3. The activation energy can be correlated with the area of the critical triangle of (La/Sr/Ba)-Al/Mg-(La/Sr/Ba). The migration path for ionic conduction of the oxygen ion was mapped out using the correlation of bulk conductivity with the A-A-B angle (β) and dc conductivity with the A-B-A angle (α). [ABSTRACT FROM AUTHOR]

We have presented the structural, elastic, electronic, phononic, and electron-phonon interaction properties of the La-based noncentrosymmetric superconductors, such as LaIrSi3, LaRhSi3, and LaPdSi3, by using the generalized gradient approximation of the density functional theory. The calculated elastic constants reveal the mechanical stability of all the studied compounds in their noncentrosymmetric structure, while the lack of inversion symmetry gives rise to lift the degeneracy of their electronic bands, except in the Γ-Z and X-P directions. The calculated Eliashberg spectral function shows that all phonon branches of these materials couple considerably with electrons, and thus, all of them make contribution to the average electron-phonon coupling parameter λ. Using the calculated values of λ and the logarithmically averaged phonon frequency ωln, the superconducting critical temperature Tc values for LaIrSi3, LaRhSi3, and LaPdSi3 are estimated to be 0.89, 2.56, and 2.40 K, respectively, which accord very well with their corresponding experimental values of 0.77, 2.16, and 2.60 K. [ABSTRACT FROM AUTHOR]

La2Mo2O9 (LMO) thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition and the resistive switching (RS) characteristics of the Au/LMO/Pt devices has been investigated. The Au/LMO/Pt devices show excellent unipolar RS characteristics with high resistance ratio between high resistance state and low resistance state (LRS), good endurance, and retention performances. The results of temperature dependence of resistance and x-ray photoelectron spectroscopy suggest that the observed RS characteristics can be explained by the formation and rupture of conducting filaments composed of oxygen vacancies. Furthermore, the plot of the reset current (IR) as a function of the third harmonic coefficient (B0) caused by Joule heating during the reset process shows scaling behavior with a power law of IR∝ B0-δ. The IR and reset power (PR) can also be scaled to the resistance in LRS (R0), i.e., IR(PR) ∝ R0-α(β). The observed scaling behaviors indicate the importance of the Joule heating for the RS characteristics of Au/LMO/Pt devices. These results demonstrate the potential application of LMO thin film in a nonvolatile memory device. [ABSTRACT FROM AUTHOR]

The electrical transport properties of La1-xSrxCoO3 (LSCO) thin films were investigated in this paper. As x increased up to 0.3, the electrical transport mechanism transferred from variable range hopping to double-exchange and the film simultaneously turned from an insulator into a conductor. Different from the bulk materials, the maximum conductivity of the film appeared at x=0.3. A novel electrical transport model was proposed to explain this unconventional phenomenon. Besides, the effects of doped Sr and oxygen vacancies on the electrical transport properties were clarified by investigated the transport behaviors of the LaCoO3, La0.7S0.3CoO3, and La0.7S0.3CoO3-ω films. We found that, when Sr was doped into the LaCoO3 film, the insulating film turns into a conductor; when oxygen atoms were removed from the La0.7S0.3CoO3 film, the conducting film goes back to an insulator. Our work could shed light on the electrical transport mechanism of the LSCO films. [ABSTRACT FROM AUTHOR]

Polystyrene film nanocomposites of 0.3mm thickness with embedded LaPO4-Pr nanoparticles (40 wt. %) have been synthesized. The luminescent and kinetic properties of these polystyrene composites with embedded LaPO4-Pr nanoparticles upon pulse X-ray excitation have been studied. The luminescence intensity of this polystyrene material significantly increases as it is loaded with inorganic LaPO4-Pr nanoparticles. Nanocomposite films reveal luminescence spectra typical for polystyrene activators (p-Terphenyl and POPOP) and two components of decay time kinetics of luminescence with 12 ns and 2.8 ns time constants, depending on nanoparticle sizes. The component with 12 ns decay constant arises due to the radiative transfer of the 5d-4f-emission of the Pr3+ ions in the LaPO4 nanoparticles to the polystyrene. The decay component with the time constant 2.8 ns originates from luminescence of polystyrene matrix excited by electrons emitted from nanoparticles due to the photoeffect. This nonradiative mechanism of energy transfer from nanoparticles to polystyrene matrices is determinative for nanoparticles, as their sizes are smaller than a mean free path of an electron. [ABSTRACT FROM AUTHOR]

The La-excess alloys La1+δ(Fe0.85Si0.15)13 (d=0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature TC. The maximum entropy change -ΔSm was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, respectively. The estimated relative cooling power for ΔH=70 kOe was 418 J/kg. The alloys show a typical NaZn13-type cubic structure, featuring a doping-induced magnetovolume effect with the increase in TC. Under the applied pressure up to 2 GPa, the TC as deduced from resistance measurements decreased linearly, ΔTC=113 (for δ=0.06) and 111K (for δ=0.09), together with a corresponding decrease of resistivity, Δp=6.1 µΩ m at room temperature for both samples. At a low pressure, the effect of spontaneous magnetostriction on TC caused by applying the pressure appeared to have a similar magnitude to that of the negative magnetovolume effect caused by La-excess doping. In comparison with other stoichiometric La(Fe1-xSix)13 compounds, the pressure in our case was shown to have a smaller influence on TC. [ABSTRACT FROM AUTHOR]

The La-excess alloys La1+δ(Fe0.85Si0.15)13 (d=0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature TC. The maximum entropy change -ΔSm was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, respectively. The estimated relative cooling power for ΔH=70 kOe was 418 J/kg. The alloys show a typical NaZn13-type cubic structure, featuring a doping-induced magnetovolume effect with the increase in TC. Under the applied pressure up to 2 GPa, the TC as deduced from resistance measurements decreased linearly, ΔTC=113 (for δ=0.06) and 111K (for δ=0.09), together with a corresponding decrease of resistivity, Δp=6.1 µΩ m at room temperature for both samples. At a low pressure, the effect of spontaneous magnetostriction on TC caused by applying the pressure appeared to have a similar magnitude to that of the negative magnetovolume effect caused by La-excess doping. In comparison with other stoichiometric La(Fe1-xSix)13 compounds, the pressure in our case was shown to have a smaller influence on TC. [ABSTRACT FROM AUTHOR]

A series of LaAlO3 thin films with different thicknesses were deposited by pulsed laser deposition at temperatures from 720 °C to 800 °C. The results from grazing incidence x-ray diffraction and reciprocal space mapping indicate that a thin layer of LaAlO3 adjacent to the SrTiO3 substrate remains almost coherently strained to the substrate, while the top layer starts to relax quickly above a certain critical thickness, followed by a gradual relaxation at larger film thickness when they are grown at lower temperatures. The atomic force microscopy results show that the fast relaxation is accompanied by the formation of cracks on the film surface. This can be ascribed to the larger energy release rate when compared with the resistance of LaAlO3 to cracking, according to calculations from the Griffith fracture theory. For films grown at 720 °C, a drop in sheet resistance by two orders of magnitude is observed when the top layer starts to relax, indicating a relationship between the strain and the conductivity of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. The strain engineered by growth temperature provides a useful tool for the manipulation of the electronic properties of oxide heterointerfaces. [ABSTRACT FROM AUTHOR]

We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO3 (a-LHO) thin films for non-volatile resistive random access memory applications. Nonpolar resistive switching (RS) was achieved in Pt/a-LHO/Pt memory cells with all four possible RS modes (i.e., positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high RON/ROFF ratios (in the range of ~104-105) and non-overlapping switching voltages (set voltage, VON~±63.6-4.2V and reset voltage, VOFF~±1.3-1.6V) with a small variation of about 65-8%. Temperature dependent current-voltage (I-V) characteristics indicated the metallic conduction in low resistance states (LRS). We believe that the formation (set) and rupture (reset) of mixed conducting filaments formed out of oxygen vacancies and metallic Ho atoms could be responsible for the change in the resistance states of the memory cell. Detailed analysis of I-V characteristics further corroborated the formation of conductive nanofilaments based on metal-like (Ohmic) conduction in LRS. Simmons-Schottky emission was found to be the dominant charge transport mechanism in the high resistance state. [ABSTRACT FROM AUTHOR]

Correlation of structure and ion conduction of La2-xYxMo2O9 (0≤x≤0.2) has been investigated. The cubic symmetry with space group P213 and other structural parameters are obtained from Rietveld refinement of X-ray diffraction patterns of Y doped samples. The average lanthanum-oxygen and molybdenum-oxygen distances are obtained from the electron density contour plot. The transmission electron microscopic study confirms the cubic nature of the samples and also provides an estimate of thickness of the grain boundary. The scanning transmission electron microscope energy dispersive spectrometer mapping confirms the different orientations of grains. The composition dependence of the ionic conductivity has been correlated with that of O2 and O3 site occupancies in the [O1La3Mo] antitetrahedral unit. The different vibrational modes in the low frequency region due to vibration of Mo-O bands are confirmed from the analysis of FTIR and Raman spectra. The full widths at half maximum of most of the Mo-O bands are found to be independent of Y doping. Additionally, the shifts in the position of Raman bands are correlated with unit cell parameter using Grüneisen constant [ABSTRACT FROM AUTHOR]

We investigate magnetoresistance, ρc, of single-crystal bilayer lanthanum manganites (La1-zNdz)1.4Sr1.6Mn2O7 (z=0 and 0.1) at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La1.4Sr1.6Mn2O7 manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab sample plane at the temperatures T<60 K, along with the negative magnetoresistance typical of all the substituted lanthanum manganites. In the (La0.9Nd0.1)1.4Sr1.6Mn2O7 sample, the positive magnetoresistance effect is observed at temperatures of 60-80K in an applied field parallel to the c axis. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic structure of the investigated compounds. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of an experimental investigation on the magnetocaloric properties of hydrogenated La(Fe-Mn-Si)13-H with Mn substituting Fe to finely tune the transition temperature. We measured the specific heat under magnetic field cp(H, T) and the magnetic field induced isothermal entropy change Δs(H, T) of a series of compounds by direct Peltier calorimetry. Results show that increasing Mn from 0.06 to 0.46 reduces the transition temperature from 339K to 270K whilst the total entropy change due to a 1.5 T field is depressed from 18.7 J kg-1K-1 to 10.2 J kg-1K-1 and the thermal hysteresis similarly is reduced from 1.5K to zero. In the paper, we interpret the results in terms of a magnetic phase transition changing from the first to the second order with increasing Mn content, and we discuss the value of the results for magnetic cooling applications. [ABSTRACT FROM AUTHOR]

The gas phase emitter effect increases the lamp lifetime by lowering the work function and, with it, the temperature of the tungsten electrodes of metal halide lamps especially for lamps in ceramic vessels due to their high rare earth pressures. It is generated by a monolayer on the electrode surface of electropositive atoms of certain emitter elements, which are inserted into the lamp bulb by metal iodide salts. They are vaporized, dissociated, ionized, and deposited by an emitter ion current onto the electrode surface within the cathodic phase of lamp operation with a switched-dc or ac-current. The gas phase emitter effect of La and the influence of Na on the emitter effect of La are studied by spatially and phase-resolved pyrometric measurements of the electrode tip temperature, La atom, and ion densities by optical emission spectroscopy as well as optical broadband absorption spectroscopy and arc attachment images by short time photography. An addition of Na to the lamp filling increases the La vapor pressure within the lamp considerably, resulting in an improved gas phase emitter effect of La. Furthermore, the La vapor pressure is raised by a heating of the cold spot. In this way, conditions depending on the La vapor pressure and operating frequency are identified, at which the temperature of the electrodes becomes a minimum. [ABSTRACT FROM AUTHOR]

Magnetotransport properties of La2/3Sr1/3MnO3/LaAlO3/Pt tunnel junctions have been thoroughly analyzed, as a function of temperature and magnetic field, to test the suitability of LaAlO3 for insulating barriers and spin injection processes. The insulating behavior of LaAlO3 maintained down to 1-2nm (corresponding to 4-5 unit cells) renders this material useful as tunnel barrier. The temperature dependence of the junction resistance, R(T), down to 200K confirms direct tunneling as the dominant conduction channel. The barrier parameters of the junctions, φ0 and s, are estimated using Simmons' model in the intermediate voltage range. The energy of the barrier was estimated to be φ0~0.4V at room temperature. The dependence of R(T) and φ0 on the magnetic field shows an anisotropic tunneling magnetoresistance of ~4% at low T when changing the direction of the magnetization with respect to the current flow. [ABSTRACT FROM AUTHOR]

Perovskite-structured Ba1-xLaxSnO3 (x=0-0.10) films have been directly grown on (0001) sapphire substrates by a sol-gel method. Optical properties and bandgap energy of the films have been investigated by transmittance spectra from 10K to 450 K. It indicates that these films exhibit a high transmission of more than 80% in the visible region. With increasing temperature, there is a significant bandgap shrinkage of about 0.5 eV for lightly La doping (x⩽0.04) films. For heavily La doping concentration (x⩾0.06), the bandgap remains nearly stable with the temperature and La composition. This is due to the fact that the lattice expansion caused by La doping is close to the saturation for the film doped with x=0.06. Moreover, temperature dependent conductivity behavior shows a similar pattern, which suggests that the doping concentration of La-doped BaSnO3 (BLSO) films has a saturated state. The La introduction can modify the Sn 5s-O 2p antibonding state and the nonbonding O 2p orbital, which remarkably affect the electronic bandgap of the BLSO films. [ABSTRACT FROM AUTHOR]

We report that epitaxial strain and chemical doping can be used cooperatively to tune the sharpness of metal-insulator transition (MIT) in epitaxial (La1_xPrx )0.67Ca0.33MnO3 (LPCMO) films. Compared to multiple MITs in anisotropically strained LPCMO/(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (001)C (LSAT) films with a phase-separated ground state, the lattice-matched LPCMO/ NdGaO3(110)Or (NGO) films show a sharp MIT near the Curie temperature (TC), with a ferromagnetic-metallic ground state. The sharpness of MIT, as evaluated by the temperature coefficient of resistance (TCR), can be two times larger in LPCMO/NGO films than in LPCMO/LSAT films. Moreover, for LPCMO/NGO films, TCR greatly relies on the Pr doping level x, where a maximum TCR value of 88.17% K-1 can be obtained at x = 0.25, but shows less dependence on the film thicknesses. These results suggest that the combination of epitaxial strain and chemical doping could be employed to control not only the ground state of the manganite films, but the sharpness of MIT at various TC, providing the feasibility to design manganite-based infrared devices in a broad temperature range. [ABSTRACT FROM AUTHOR]

In this work, we have studied electrical conductivity and dielectric properties of polycrystalline La2_xYxMo2O9 (0.05 = x = 0.3) compounds in the temperature range from 358 K to 1088 K and the frequency range from 10 Hz to 3 GHz. The bulk and grain boundary contributions to the overall conductivity of these compounds show Arrhenius type behavior at low temperatures. The random free-energy barrier model has been used to analyze the frequency dependence of the conductivity. The charge carrier relaxation time and its activation energy have been determined from the analysis of the conductivity spectra using this model. The results obtained from the random free-energy barrier model satisfy Barton-Nakajima-Namikawa relation. The conduction mechanism has been also predicted using random free-energy barrier model and the scaling formalism. We have observed that the dielectric relaxation peaks arise from the diffusion of oxygen ions via vacancies. [ABSTRACT FROM AUTHOR]

Single crystals of LaMn0.5Co0.5O3 belonging to the ferromagnetic-insulator and distorted perovskite class were grown using a four-mirror optical float zone furnace. The as-grown crystal crystallizes into an orthorhombic Pbnm structure. The spatially resolved 2D Raman scan reveals a strain-induced distribution of transition metal (TM)-oxygen (O) octahedral deformation in the as-grown crystal. A rigorous annealing process releases the strain, thereby generating homogeneous octahedral distortion. The octahedra tilt by reducing the bond angle TM-O-TM, resulting in a decline of the exchange energy in the annealed crystal. The critical behavior is investigated from the bulk magnetization. It is found that the ground state magnetic behavior assigned to the strain-free LaMn0.5Co0.5O3 crystal is of the 3D Heisenberg kind. Strain induces mean field-like interaction in some sites, and consequently, the critical exponents deviate from the 3D Heisenberg class in the as-grown crystal. The temperature-dependent Raman scattering study reveals strong spin-phonon coupling and the existence of two magnetic ground states in the same crystal. [ABSTRACT FROM AUTHOR]

In the present work, we have illustrated the physics of the multifunctional characteristics of nano-crystalline LaFeO3 powder prepared using auto-combustion synthesis. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. The temperature dependence of dielectric constant of pure LaFeO3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. The dielectric relaxation of LaFeO3 correlates well with small polaron conduction. The occurrence of polarization hysteresis in LaFeO3 (with centro-symmetric Pnma space group) is thought to be spin current induced type. The canting of the Fe3+ spins induce weak ferromagnetism in nano-crystalline LaFeO3. Room temperature saturation magnetization of pure LaFeO3 is reported to be 3.0 emu/g. Due to the presence of both ferromagnetic as well as polarization ordering, LaFeO3 behaves like a single phase multiferroic ceramics. The magneto-electric coupling in this system has been demonstrated through the magneto-dielectric measurements which yield about 0.8% dielectric tuning (at 10 kHz) with the application of 2 T magnetic field. As a typical application of the synthesized nano-crystalline LaFeO3 powder, we have studied its butane sensing characteristics. The efficient butane sensing characteristics have been correlated to their catalytic activity towards oxidation of butane. Through X-ray photoelectron spectroscopy analyses, we detect the surface adsorbed oxygen species on LaFeO3 surface. Surface adsorbed oxygen species play major role in their low temperature butane sensing. Finally, we have hypothesized that the desorbed H2O and O2 (originate from surface adsorbed hydroxyl and oxygen) initiate the catalytic oxidative dehydrogenation of n-butane resulting in weakening of the electrostatics of the gas molecules. [ABSTRACT FROM AUTHOR]

The atomic structures of SrTiO3 (STO)/LaNiO3 (LNO)/STO heterostructure interfaces were investigated by spherical aberration-corrected (CS) (scanning) transmission electron microscopy. Atomic displacement and lattice distortion measurements and electron energy loss spectroscopy (EELS) were used to quantitatively analyze the distortion of the interfacial octahedra and the bond length at the interfaces. Combined with high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy analyses, two distinct interfacial atomic terminating layers are unambiguously determined. Ensuing quantitative HRTEM measurements revealed that the Ni-O bond length in the interfacial octahedral is elongated at the bottom interface (–NiO2-SrO–). Atomic displacement shows structural relaxation effects when crossing the interfaces and lattice distortions across the interface is more pronounced in LNO than in STO. The Ti/O atomic ratio, La and Ti relative atomic ratio as derived by EELS quantification indicate non-stoichiometric composition at the interfaces. Distinct fine structures of Ti-L2,3 edge and O-K edge at the bottom and top interfaces are observed. By comparison, we are able to estimate Ti valency at both interfaces. Combining the structural distortions and Ti valency, the polar discontinuity and charge transfer at the interfaces are discussed. [ABSTRACT FROM AUTHOR]

Structural, electronic, vibrational, and dielectric properties of LaBGeO5 with the stillwellite structure are determined based on ab initio density functional theory. The theoretically relaxed structure is found to agree well with the existing experimental data with a deviation of less than 0.2%. Both the density of states and the electronic band structure are calculated, showing five distinct groups of valence bands. Furthermore, the Born effective charge, the dielectric permittivity tensors, and the vibrational frequencies at the center of the Brillouin zone are all obtained. Compared to existing model calculations, the vibrational frequencies are found in much better agreement with the published experimental infrared and Raman data, with absolute and relative1 firms values of 6.04 cm-1, and 1.81%, respectively. Consequently, numerical values for both the parallel and perpendicular components of the permittivity tensor are established as 3.55 and 3.71 (10.34 and 12.28), respectively, for the high-(low-)frequency limit. [ABSTRACT FROM AUTHOR]

Cation intermixing at functional oxide interfaces remains a highly controversial area directly relevant to interface-driven nanoelectronic device properties. Here, we systematically explore the cation intermixing in epitaxial (001) oriented multiferroic bismuth ferrite (BFO) grown on a (001) lanthanum aluminate (LAO) substrate. Aberration corrected dedicated scanning transmission electron microscopy and electron energy loss spectroscopy reveal that the interface is not chemically sharp, but with an intermixing of ~2 nm. The driving force for this process is identified as misfit-driven elastic strain. Landau-Ginzburg-Devonshire-based phenomenological theory was combined with the Sheldon and Shenoy formula in order to understand the influence of boundary conditions and depolarizing fields arising from misfit strain between the LAO substrate and BFO film. The theory predicts the presence of a strong potential gradient at the interface, which decays on moving into the bulk of the film. This potential gradient is significant enough to drive the cation migration across the interface, thereby mitigating the misfit strain. Our results offer new insights on how chemical roughening at oxide interfaces can be effective in stabilizing the structural integrity of the interface without the need for misfit dislocations. These findings offer a general formalism for understanding cation intermixing at highly strained oxide interfaces that are used in nanoelectronic devices. [ABSTRACT FROM AUTHOR]

The luminescence from europium doped lanthanum trifluoride (Eu3+:LaF3) nano-crystals can be greatly enhanced by capping with β-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm-2, the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms. [ABSTRACT FROM AUTHOR]

We have studied the behavior of LaFeO3 under pressure (P) using density functional theory (DFT) and atomistic simulations. Ground state structural properties of LaFeO3 are correctly described by atomistic simulations. The effect of high pressure shows that there is an isotropic compression up to 100 GPa. However, DFT calculations show that within pressure range 0 < P < 32.4 GPa, LaFeO3 retains its ground state electronic structure. On the other hand, at P ∼32.4 GPa high to low spin magnetic phase transition is observed, which is accompanied by 6.9% volume collapse of LaFeO3 unit cell, while retaining the ground state orthorhombic crystal structure, i.e., isostructural phase transition. Furthermore, the band gap is closed leading insulator to metal transition. This differing behavior observed by the two techniques can be attributed to the omission of magnetic effects in static simulations. The simultaneous magnetic, electrical, and structural (volume collapse) phase transitions of LaFeO3 under compression as revealed by DFT calculations corroborate experimental findings. From these results, we can elaborate the mechanism of phase transition in LaFeO3: increasing crystal field induces a high spin to low spin transition, which in turn drives the electrical transitions and volume collapse. [ABSTRACT FROM AUTHOR]

Different vortex penetration regimes have been registered in the output voltage signal of a magnetometer when single microwave pulses are applied to an epitaxial overdoped La2-xSrxCuO4 thin film in a perpendicular dc magnetic field. The onset of a significant variation in the sample magnetization which exists below threshold values of temperature, dc magnetic field, and pulse duration is interpreted as an avalanche-type flux penetration. The microwave contribution to the background electric field suggests that the nucleation of this fast vortex motion is of electric origin, which also guarantees the occurrence of vortex instabilities under adiabatic conditions via the enhancement of the flux flow resistivity. Flux creep phenomena and heat transfer effects act as stabilizing factors against the microwave-pulse-induced fast flux diffusion. [ABSTRACT FROM AUTHOR]

The scintillation response of LaBr3:Ce scintillation crystals was studied as function of temperature and Ce concentration with synchrotron X-rays between 9 keV and 100 keV. The results were analyzed using the theory of carrier transport in wide band gap semiconductors to gain new insights into charge carrier generation, diffusion, and capture mechanisms. Their influence on the efficiency of energy transfer and conversion from X-ray or γ-ray photon to optical photons and therefore on the energy resolution of lanthanum halide scintillators was studied. From this, we will propose that scattering of carriers by both the lattice phonons and by ionized impurities are key processes determining the temperature dependence of carrier mobility and ultimately the scintillation efficiency and energy resolution. When assuming about 100 ppm ionized impurity concentration in 0.2% Ce3+ doped LaBr3, mobilities are such that we can reproduce the observed temperature dependence of the energy resolution, and in particular, the minimum in resolution near room temperature is reproduced. [ABSTRACT FROM AUTHOR]

Remarkable enhancement/reduction of light emission and competition among different wavebands with rare earth doped lanthanum lead zirconate titanate ceramics were observed in a corona atmosphere caused by an externally applied electric field. Quantum-mechanical analyses, based on variation of structural symmetry of the unit cell and hence the crystal field due to electrostriction, were given to elucidate the effect. Apart from the symmetry of crystal field, the obvious contribution from the optoenergy storage and weak localization of light involved were discussed. These results are promising in designing and implementation of lasers and sensors. [ABSTRACT FROM AUTHOR]

Bilayers of La0.7Sr0.3MnO3/NiO and LaMnO3/NiO were prepared and magnetic exchange coupling investigated in these bilayers, where the Curie temperature of the ferromagnetic (FM) layer is lower than the Néel temperature of the antiferromagnetic layer. After small-field cooling, the LSMO/NiO bilayer exhibits an exchange bias with field HEB = 60 Oe, whereas the LMO/NiO sample shows weak magnetic interaction (∼22 Oe). The unconventional exchange bias in LSMO/NiO bilayer vanishes as temperature rises above 50 K. The weak magnetic interaction at the LMO/NiO interface is due to a larger Hubbard parameter value and smaller transfer integral value in the Mott insulator LMO compared with that for the FM conductor LSMO. The valence states of Mn and Ni ions across the interfaces for LSMO/NiO and LMO/NiO have been studied using X-ray photoelectron spectroscopy. We speculate that the FM interaction between Ni2+ and Mn4+ gives rise to magnetic regions that pin the ferromagnetic LSMO layer. [ABSTRACT FROM AUTHOR]

We have studied the dynamic and static critical behavior of spin glass transition in insulating La0.9Sr0.1CoO3 single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature (Tf). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant τ0=1.6(9)×10-12 s, the dynamic critical exponent zν=9.5(2), and a frequency dependence factor K=ΔTf/Tf(Δlogf)=0.017, indicating that the sample enters into a canonical spin-glass phase below Tf = 34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of Tf through the static scaling hypothesis yields critical exponents β = 0.89(1) and γ = 2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement, we have constructed the H-T phase diagram which represents the field evolution of two characteristic temperatures: the upper one, Tw(H), indicates the onset of spin freezing in a uniform external field H, while the lower one, Ts(H), marks the onset of strong irreversibility of the frozen state. The low field Ts(H) follows the critical line suggested by d'Almeida-Thouless model for canonical spin glass, whereas the Tw(H) exhibits a re-entrant behavior with a maximum in the Tw(H) at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The reentrant behavior of the GT line resembles that predicted theoretically for n-component vector spin glasses in the presence of a uniaxial anisotropy field. [ABSTRACT FROM AUTHOR]

Nanoparticles with sizes <10 nm were fabricated and characterized for their nanocomposite radiation detector properties. This work investigated the properties of several nanostructured radiation scintillators, in order to determine the viability of using scintillators employing nanostructured lanthanum trifluoride. Preliminary results of this investigation are consistent with the idea that these materials have an intrinsic response to nuclear radiation that may be correlated to the energy of the incident radiation. [ABSTRACT FROM AUTHOR]

Perovskite oxide LaFeO3, as a novel candidate for the electrode of Ni/MH battery, holds high specific capacity and good cyclical durability at elevated temperatures. However, the poor electrochemical kinetics is a bottleneck for the application of this type of material. By use of nano-structured materials, there are greatly enhanced values of exchange current density I0 and hydrogen diffusion coefficient D, which resulted in an improvement of electrochemical kinetics, a much higher specific capacity and excellent stability during cycling for nano-structured LaFeO3. In theory, there is a significant possibility of further advancing the hydrogen reaction kinetics of perovskite type oxides for Ni/MH battery. [ABSTRACT FROM AUTHOR]

The solution behavior of dopants, Si, La, and N, in HfO2 polymorphs, monoclinic, tetragonal, and cubic was investigated by using a first principles calculation based on density functional theory within the local density approximation. It was found that the Si and La solutions are more preferable under oxidization atmosphere than reduction atmosphere, and the most efficient nitridation condition for the HfO2 is NO/NO2 atmosphere. By comparing the energy difference between the monoclinic and the tetragonal phases, it was found that the energy difference is decreased by the Si or La doping, whereas influence of the N doping is small, indicating that the phase transition from the monoclinic to tetragonal phase would be enhanced by the Si or La doping. [ABSTRACT FROM AUTHOR]

A study of the magnetic, electrical resistivity and hyperfine properties of polycrystalline La2RuO5 compounds is presented in this work. This compound forms in a monoclinic phase (space group P21/c). Magnetic susceptibility measurements yield an effective magnetic moment which is consistent with spin S = 1 of Ru ions, and a negative paramagnetic Curie temperature which indicates the presence of antiferromagnetic interactions. Below T ∼ 165 K, the magnetization shows a sudden decrease, precisely where the electrical resistivity shows a change in the activation energy. Room-temperature perturbed angular correlation spectrum is well fitted considering two electric-quadrupole components. The temperature dependences of electric-quadrupole frequencies and asymmetry parameters corroborate the occurrence of a phase transition at T ∼ 170 K. Moreover, below 170 K, magnetic-dipole interactions, which coexist with electric-quadrupole interactions, are observed at Ru sites. This is considered as a strong evidence for the preservation of S = 1 moment of Ru ions in the triclinic phase. The temperature dependence of the magnetic hyperfine field shows an unusual behavior, not consistent with the Brillouin function, and suggests a first-order magnetic transition, associated with either a structural transition or an orbital ordering induced by the Ru-Ru pair formation. [ABSTRACT FROM AUTHOR]

The structural and optoelectronic properties of LaAlO3 under pressure have been investigated for the first time using the highly accurate all electrons full potential linearized augmented plane wave method. The calculated lattice parameter at zero pressure is found in excellent agreement with the experimental results. Furthermore, with the increase in the external pressure, the lattice constant as well as bonds length decreases in accordance with the experimental results. The compound at zero pressure is an indirect bandgap semiconductor, while interestingly the indirect nature shifts to direct one with the increase of the pressure. The bonding in the material is of mixed covalent and ionic nature. In optical properties, frequency dependent parameters such as real and imaginary parts of dielectric function, refractive index, reflectivity, optical conductivity, absorption coefficient, and sumrules are calculated under pressure. [ABSTRACT FROM AUTHOR]

Scaled layers of HfO2 on LaGeOx on Ge grown by molecular beam deposition and their electrical properties and passivation are discussed. The interfacial LaGeOx thickness as well as the deposition temperature of the HfO2 cap are varied and the effects thereof on properties like peak mobility and interface trap distributions are compared. We report on negative threshold voltages, around -0.8 V, in combination with scaled devices with a minimum EOT of 1.4 nm, which shows beneficial characteristics for the LaGeOx passivation of Ge. The effect of various post-metallization anneals in FG and O2 is shown to improve the gate stack properties of the scaled samples, yielding higher peak mobilities with maximum values of about 120 cm2/Vs for annealed samples. The impact of LaGeOx interfacial layer thickness and HfO2 deposition temperature on the density of interface traps (Dit) distributions for as-deposited and annealed samples is discussed, and Hf in-diffusion into the LaGeOx is shown to be detrimental to its passivation of Ge. The Dit distributions are measured by the full conductance technique on MOSFETs at room temperature as well as 233 K and are then correlated with the mobilities extracted from the same devices. [ABSTRACT FROM AUTHOR]

Thin films of YBCO have been deposited on bare and La0.67Sr0.33MnO3 (LSMO) nanoparticle decorated single crystal SrTiO3 (STO) substrates. The effect of ferromagnetic LSMO nanoparticles, present at the substrate/film interface, on the superconducting properties of YBa2Cu3O7-δ (YBCO) thin film has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on the undecorated substrate, and this improvement is more significant at higher applied magnetic field. The presence of LSMO nanoparticles at YBCO/STO interface seems to introduce structural defects, which might be in the form of threading dislocations along the c-axis acting as correlated pinning centers leading to improved flux pinning properties of the YBCO thin film. The LSMO nanoparticles are ferromagnetic, which can also act as magnetic pinning centers and may result in the enhancement of flux pinning properties of the YBCO thin film deposited on the LSMO decorated STO substrate. [ABSTRACT FROM AUTHOR]

In this work, photoelectron spectroscopy is used to characterize the band alignment of lanthanum aluminate heterostructures which possess a wide range of potential applications. It is found that our experimental slope parameter agrees with theory using the metal-induced gap states model while the interface induced gap states (IFIGS) model yields unsatisfactory results. We show that this discrepancy can be attributed to the correlation between the dielectric work function and the electronegativity in the IFIGS model. It is found that the original trend, as established largely by metals, may not be accurate for larger band gap materials. By using a new correlation, our experimental data shows good agreement of the slope parameter using the IFIGS model. This correlation, therefore, plays a crucial role in heterostructures involving wider bandgap materials for accurate band alignment prediction using the IFIGS model. [ABSTRACT FROM AUTHOR]

The behavior of temperature dependences of electrical resistance and magnetoresistance of polycrystalline substituted lanthanum manganite (La0.5Eu0.5)0.7Pb0.3MnO3 at low temperatures was thoroughly studied. A broad hysteresis was found in the field dependences of electrical resistance in the low-temperature region. Above 40 K, no hysteresis feature was observed. The temperature T = 40 K corresponds to the temperature of minimum electrical resistance and the temperature TN to the antiferromagnet-paramagnet phase transition of the material of the intergrain boundaries. In this work we propose a model which explains the observed features of the ρ(T) and ρ(H) curves at temperatures below TN by the formation of a network of ferromagnet-antiferromagnet-ferromagnet tunnel contacts. [ABSTRACT FROM AUTHOR]

We have performed a systematic structural, vibrational, and optical study of LaF3:Eu3+ nanoparticles capped with oleic acid (OA) or OA and sensitized with thenoyltrifluoroacetone (TTA). The average nanoparticle size was around 11 nm for all Eu3+ concentrations. A shift in the energy of the Raman active modes is observed with increasing Eu3+ concentration that can be accounted for by a decrease in the unit cell volume. Sensitization by TTA was observed and resulted in an 18 000% increase in the photoluminescence (PL) intensity for TTA/OA capped LaF3:Eu3+ nanoparticles when compared with OA capped LaF3:Eu3+ nanoparticles. There is also a large increase in the 5D0→7F2 PL intensity, when normalized to the 5D0→7F1 PL magnetic dipole transition intensity, for TTA/OA capped nanoparticles. The changes in the PL intensities, PL lifetimes, Judd-Ofelt parameters, stimulated emission cross sections, and quantum efficiencies, for OA and TTA/OA capped LaF3:Eu3+ nanoparticles with increasing Eu3+ concentration can be accounted for by a model that separates the Eu3+ sites into sites near the surface and Eu3+ sites in the core as well as nonradiative recombination sites near the surface. The large increase in PL intensity due to TTA sensitization means that TTA capped LaF3:Eu3+ can potentially be used for applications that include optical amplification. [ABSTRACT FROM AUTHOR]

Rectifying and photoelectronic properties of the La0.67Ba0.33MnO3/SrTiO3:Nb junctions with the film thickness from d=0.5 to 30 nm have been systematically studied. It is found that the electronic transport of the junction is dominated by quantum tunneling or thermoionic emission when film thickness is below or above 1 nm. The rectifying ratio and ideality factor, correspondingly, experience a sudden change as film thickness grows from 0.5 to 1 nm and a smooth variation with film thickness above 1 nm. The threshold film thickness for the establishment of a mature depletion layer is therefore 1 nm. The photoemission properties of the junctions also exhibit a strong dependence on film thickness. As experimentally shown, the photocurrent vanishes in the zero thickness limit, and grows rapidly with the increase in film thickness until d=6 nm, where a maximal photocurrent of ∼770 nA/mm2 under the irradiance of the laser of 5 mW and 532 nm is obtained. After this maximum, an increase-to-decrease turning appears with further increasing film thickness. Taking into account the finite diffusion distance of the photocarriers and the strain-enhanced charge trapping in ultrathin film junctions, a theoretical description that well reproduces the experiment results can be obtained, which reveals the severe depression of finite diffusion distance of the extra carriers on photocurrent. The maximal diffusion distance thus obtained is ∼3.5 nm. Similar analyses have been performed for the La0.67Ca0.33MnO3/SrTiO3:Nb junctions, and the corresponding diffusion distance there is ∼1.5 nm. [ABSTRACT FROM AUTHOR]

The electrical conduction mechanism in La3Ta0.5Ga5.5O14 (LTG) was studied from the standpoint of defect formation during growth caused by the nonstoichiometry of the crystal. Since the stoichiometric composition of LTG does not coincide with the congruent composition, single crystals grown from the stoichiometric melt under an atmosphere of O2/Ar in the oxygen partial pressure range from 0.005 to 1 atm was Ta-poor. Ta vacancies were formed during the growth, and their population was predominated by the growth-pO2. With increasing temperature up to 600 °C, the Ta vacancies were ionized to yield holes, and thus the electrical conductivity of the LTG crystal varied with temperature and growth-pO2. In contrast, Ga vacancies as a carrier source would form by Ga evaporation during growth under pO2 below 0.005 atm. The growth-pO2 dependence of the electrical conductivity was opposite to the case for Ta vacancies. For the case of sintered LTG with the exact stoichiometric composition, impurity defects dominated electrical conduction below 600 °C, where the impurity concentration was higher than the cation vacancies arising from the nonstoichiometry of the sintered LTG. Thus, electrical conductivity was almost independent of the sintering atmosphere of pO2. Above 700 °C, the dominant carrier in both single crystal and sintered LTG was ions related to oxygen defects formed by the anion Frenkel reaction. [ABSTRACT FROM AUTHOR]

Metal-oxide-semiconductor capacitors and n-channel metal-oxide-semiconductor field-effect transistors with La2O3 gate dielectric were fabricated. The positive bias temperature instability was studied. The degradation of threshold voltage (ΔVT) showed an exponential dependence on the stress time in the temperature range from 25 to 75 °C. The degradation of subthreshold slope (ΔS) and gate leakage (IG) with stress voltage was also measured. The degradation of VT is attributed to the oxide trap charges Qot. The extracted activation energy of 0.2 eV is related to a degradation dominated by the release of atomic hydrogen in La2O3 thin films. [ABSTRACT FROM AUTHOR]