Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

Electrical properties of La0.6Ca0.4MnO3–Bi3.4Nd0.6Ti3O12 thin films derived by a sol–gel process

Magnetoelectric (ME) xLa_0.6Ca_0.4MnO₃–(1 ? x)Bi_3.4Nd_0.6Ti₃O₁₂ (LCMO–BNT) composite thin films have been prepared by a sol–gel process and spin-coating technique. The effects of LCMO content on the microstructure, leakage current density, ferroelectric properties, fatigue endurance and ME voltage coefficient of LCMO–BNT thin films derived by sol–gel method were studied. It was found that the composite thin films have better fatigue endurance properties and lower leakage current densities compared with pure BNT thin films, as well as large ME voltage coefficients.     

Electrochemical characteristics of cathodes based on perovskites modified by ceria

A system consisting of a solid oxide electrolyte of the Ce_0.9Gd_0.1O_{2 − x} (CGO) composition in contact with a two-layer cathode based on a nonstoichiometric composition (La_0.8Sr_0.2)_0.95MnO_{3 ± δ} (LSM1) and a stoichiometric perovskite La_0.8Sr_0.2MnO_{3 ± δ} (LSM2) is prepared by the tape-casting process. It was shown that the best electrochemical characteristics are achieved for a three-layer system LSM2/{CGO-LSM1}/CGO sintered at 1410°C. The use of Ce-modified perovskites La_0.8Sr_0.2MnO_{3 ± δ} and La_0.6Sr_0.6CoO_{3 ± δ} as the collector layer of two-layer electrodes allows the electrochemical characteristics at moderately high temperatures (600–750°C) to be improved.     

Magnetocapacitance and impedance spectroscopy of Ba0.7Sr0.3TiO3/La0.67Sr0.33MnO3 and Ba0.8Sr0.2TiO3/La0.67Sr0.33MnO3 thin film heterostructures

The paper discuses synthesis of Ba_0.7Sr_0.3TiO₃/La_0.67Sr_0.33MnO₃ and Ba_0.8Sr_0.2TiO₃/La_0.67Sr_0.33MnO₃ thin film heterostructures by sol–gel (citrate gel route) method. The XRD spectra are determined for confirmation of crystalline phases of Ba_0.7Sr_0.3TiO₃, Ba_0.8Sr_0.2TiO₃ and La_0.67Sr_0.33MnO₃ thin films. The observed variation of Cp, tan δ, magnetocapacitance (Mc), real part of dielectric constant ε′, imaginary part of dielectric constant ε″as a function of frequency, magnetoresistance R(H) and magnetoimpedance Z(H) are presented in the paper. Further the observed impedance spectra as a function of frequency f is also presented in the paper. The observed variation of Mc is qualitatively correlated with the stress induced effect and magnetoresistasnce effect occurring simultaneously.     

Direct Observation of Oxygen Dissociation on Non‐Stoichiometric Metal Oxide Catalysts

Oxygen dissociation on metal oxides is a key reaction step, limiting the efficiency of numerous technologies. The complexity of the multi‐step oxygen reduction reaction (ORR) makes it difficult to investigate the oxygen dissociation step independently. Direct observation of the oxygen dissociation process is described, quantitatively, on perovskites La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ and (La_0.8Sr_0.2)_0.95MnO_3±δ, using gas‐phase isotope‐exchange with a 1:1 ¹⁶O₂:¹⁸O₂ ratio. Oxygen transport mechanisms between gas–surface reactions and surface–bulk exchange are deconvoluted. Our findings show that regardless of participation of lattice oxygen, La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ is better at oxygen dissociation than (La_0.8Sr_0.2)_0.95MnO_3±δ. Heteroexchange, involving lattice oxygen, dominates on La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐δ. In contrast, (La_0.8Sr_0.2)_0.95MnO_3±δ shows both homoexchange and heteroexchange, with the latter only happening above 600 °C. Using a 1:1 isotope mixture, a simple method is presented for separation of the oxygen dissociation step from the overall ORR.     

Reverse micellar synthesis and properties of nanocrystalline GMR materials (LaMnO3, La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3): Ramifications of size considerations

Nanoparticles of complex manganites (viz. LaMnO₃, La_0.67Sr_0.33MnO₃ and La_0.67Ca{0.33}MnO₃) have been synthesized using the reverse micellar route. These manganites are prepared at 800‡C and the monophasic nature of all the oxides has been established by powder X-ray diffraction studies. TEM studies show an average grain size of 68, 80 and 50 nm for LaMnO₃, La_0.67Sr_0.33MnO₃ and La_0.67Ca{0.33}MnO₃respectively. Ferromagnetic ordering is observed at around 250 K for LaMnO₃, 350 K for La_0.67Sr_0.33MnO₃ and 200 K for La_0.67Ca{0.33}MnO₃. These Curie temperatures correspond well with those reported for bulk materials with similar composition.     

Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

A conductive oxide as an O2 evolution anode for the electrolytic reduction of metal oxides

The feasibility of applying the conductive oxide, La_0.33Sr_0.67MnO₃, as an O₂ evolution electrode in an electrochemical system was investigated. The La_0.33Sr_0.67MnO₃ anode was able to electrochemically reduce UO₂ to metallic U in a Li₂O-containing LiCl molten salt electrolyte with O₂ evolution. Although the La_0.33Sr_0.67MnO₃ anode remained stable during the reaction, its long-term stability should be further investigated.     

Exoemission near phase transitions of epitaxial films of manganites with colossal magnetic resistance

Intense exoemission near phase transitions of epitaxial films of the La_0.16Sr_0.84MnO₃ and La_0.35Pr_0.35Sr_0.3MnO₃, manganites, which exhibit the colossal magnetic resistance (CMR), is detected in a wide temperature range from 278 to 623 K including the Curie temperature. The role of the absorbed and lattice oxygen in the exoemission and CMR phenomena is discussed. The aftereffect of the magnetic field directed along the film plane on the intensity of photostimulated exoemission is discussed.     

Influence of the mobility of oxygen on the reactivity of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskites in methane oxidation

Radically different dependences of the activity of La_{1 − x} Sr _x MnO₃ (x = 0−0.5) perovskites in methane oxidation on the degree of substitution of strontium for lanthanum are observed for low and high temperatures. Unsubstituted LaMnO₃ exhibits the highest activity in the temperature range from 300 to 500°C, while the sample with the maximum degree of substitution (La_0.5Sr_0.5MnO₃) shows the highest activity at higher temperatures of 700–900°C. In the low temperature region, the activity of La_{1t - x} Sr _x MnO₃ is determined by the amount of weakly bound (overstoichiometric) oxygen, which is formed in cation-deficient lattices and is characterized by a thermal desorption peak with T _max = 705°C. At higher temperatures (800–900°C), the strongly bound oxygen of the catalyst lattice is involved in the formation of the reaction products under both unsteady- and steady-state conditions. As a consequence, the catalytic activity in methane oxidation correlates with the apparent rate constant of oxygen diffusion in the oxide bulk.     

Real time study of hybrid sol-gel photopolymerization by UV light

Polycrystalline La_0.67 (Sr_1-x Cd _x )_0.33MnO₃ (LSCMO x = 0, 1/8, 2/8, 3/8, 4/8) films were fabricated on Si(100) single crystal substrates by the sol–gel and the rapid annealing process. According to the field-emission scan electron microscopy (FE-SEM) observation and X-ray (XRD) diffraction studies, all the samples are single phase. We also prepared a series of samples by fixing the ratio of La at 0.67. It is shown that with increase of the doping amount x in La_0.67(Sr_1-x Cd _x )_0.33MnO₃, the average A-site cation radius 〈A〉 decreases, the temperature of metal-insulator transition (T_MI) decreases monotonically, ρ and magnetoresistance (MR) values increase dramatically, which can be explained by the lattice effects. The enhanced MR effect at low temperature for the LSCMO film is attributed to the suppression of the spin dependent scattering of polarized electrons at the grain boundaries. The low-field magnetoresistance values under 0.3 T are observed to be 2.48% (x = 0) at 300 K and 37.5% (x = 4/8) at 85 K, respectively.     

Magnetoelectric Bi3.25Nd0.75Ti3O12–La0.6Ca0.4MnO3 composite thin films derived by SOL–GEL method

Magnetoelectric (ME) Bi_3.25Nd_0.75Ti₃O₁₂–La_0.6Ca_0.4MnO₃ (BNT–LCMO) composite thin films were deposited on Pt/Ti/SiO₂/Si(100) substrates by a simple SOL–GEL method and spin-coating process with two different deposition sequences: BNT/LCMO/Pt/Ti/SiO₂/Si(BLP) and LCMO/BNT/Pt/Ti/SiO₂/Si(LBP). Our results show the composite thin films exhibit both good ferroelectric and magnetic properties, as well as a ME effect. BLP thin films have larger maximum ME voltage coefficient values than LBP structured thin films. The deposition sequence has a notable effect on the ferroelectric and magnetic properties and ME coupling behavior of the bi-layer thin films.     

The synthesis and complex anion-vacancy ordered structure of La0.33Sr0.67MnO2.42

The low-temperature topotactic reduction of La_0.33Sr_0.67MnO₃ with NaH results in the formation of La_0.33Sr_0.67MnO_2.42. A combination of neutron powder and electron diffraction data show that La_0.33Sr_0.67MnO_2.42 adopts a novel anion-vacancy ordered structure with a 6-layer OOTOOT' stacking sequence of the ‘octahedral’ and tetrahedral layers (Pcmb, a=5.5804(1) Å, b=23.4104(7) Å, c=11.2441(3) Å). A significant concentration of anion vacancies at the anion site, which links neighbouring ‘octahedral’ layers means that only 25% of the ‘octahedral’ manganese coordination sites actually have 6-fold MnO₆ coordination, the remainder being MnO₅ square-based pyramidal sites. The chains of cooperatively twisted apex-linked MnO₄ tetrahedra adopt an ordered -L-R-L-R- arrangement within each tetrahedral layer. This is the first published example of a fully refined structure of this type which exhibits such intralayer ordering of the twisted tetrahedral chains. The rationale behind the contrasting structures of La_0.33Sr_0.67MnO_2.42 and other previously reported reduced La_1−xSr_xMnO_3−y phases is discussed.     

Magnetic properties of quasi-two-dimensional La1−xSr1+xMnO4 and the evolution of itinerant electron ferromagnetism in the SrO · (La1−xSrxMnO3)n system

Quasi-two-dimensional oxides of the La_1−xSr_1+xMnO₄ system, possessing the K₂NiF₄ structure, show no evidence for ferromagnetic ordering in contrast to the corresponding three-dimensional La_1−xSr_xMnO₃ perovskites. Instead, there is an increasing tendency toward antiferromagnetic ordering with increasingx in La_1−xSr_1+xMnO₄. Furthermore, these oxides are relatively high-resistivity materials over the entire compositional range. Substitution of Ba for Sr in La_0.5Sr_1.5MnO₄ decreases the ferromagnetic interaction. Increasing the number of perovskite layers in SrO · (La_1−xSr_xMnO₃)_n causes an increase in electrical conductivity as well as ferromagnetic interaction. The oxide becomes a highly conducting ferromagnet whenn ≥ 2.     

The solid-state thermal decomposition of Sr3[La(C2O4)3(H2O)2]2·11H2O

Strontium(II)diaquatris(oxalato)lanthanate(III)unidecahydrate, Sr₃[La(C₂O₄)₃(H₂O)₂]₂·11H₂O, has been synthesized and characterized by elemental, IR and electronic spectral studies. Thermal studies (TG, DTG and DTA) in air showed that all the crystal and coordinated water molecules are removed at ca. 225 °C. The final end product at 1,000 °C was shown to be a mixture of mainly SrCO₃, Sr₃La₄O₉ and La₂Sr₂O₅ along with oxides and carbides of both the metal, through the formation of an intermediate mixture of likely SrC₂O₄ and La₂(C₂O₄)_2.8 at 282 °C, and SrCO₃ and La₂O(CO₃)₂ at 540 °C. The multi-step dehydration and decomposition of the compound has been explored from the DSC study in nitrogen up to 670 °C, and the evaluated kinetic parameters are discussed.     

Nano-sized La0.8Sr0.2MnO3 as oxygen reduction catalyst in nonaqueous Li/O2 batteries

Nano-sized La_0.8Sr_0.2MnO₃ prepared by the polyethylene glycol assisting sol–gel method was applied as oxygen reduction catalyst in nonaqueous Li/O₂ batteries. The as-synthesized La_0.8Sr_0.2MnO₃ was characterized by X-ray diffraction (XRD), scanning electron microscopy, and Brunauer–Emmet–Teller measurements. The XRD results indicate that the sample possesses a pure perovskite-type crystal structure, even sintered at a temperature as low as 600 °C, whereas for solid-state reaction method it can only be synthesized above 1,200 °C. The as-prepared nano-sized La_0.8Sr_0.2MnO₃ has a specific surface area of 32 m² g⁻¹, which is much larger than the solid-state one (1 m² g⁻¹), and smaller particle size of about 100 nm. Electrochemical results show that the nano-sized La_0.8Sr_0.2MnO₃ has better catalytic activity for oxygen reduction, higher discharge plateau and specific capacity.     

Thickness Impacts of Vacancy Defects in Epitaxial La0.7Sr0.3MnO3Thin Films Using Slow Positron Beam

Thickness effects of thin La_0.7Sr_0.3MnO₃ (LSMO) films on (LaAlO₃)_0:3(Sr₂AlTaO₆)_0:7 sub-strates were examined by a slow positron beam technique. Doppler-broadening line shape parameter S was measured as a function of thickness and differnt annealing conditions. Re-sults reveal there could be more than one mechanism to induce vacancy-like defects. It was found that strain-induced defects mainly influence the S value of the in situ oxygen- ambience annealing LSMO thin films and the strain could vanish still faster along with the increase of thickness, and the oxygen-deficient induced defects mainly affect the S value of post-annealing LSMO films.     

Microstructure,magnetoelectric properties and leakage mechanisms of La0.7Ca0.3MnO3/Bi3.15Nd0.85TiO3 composite thin films

A series of high quality Bi_3.15Nd_0.85TiO₃ (BNT) ferroelectric thin films and La_0.7Ca_0.3MnO₃/Bi_3.15Nd_0.85TiO₃ (LCMO/BNT) multiferroic composite thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD) method. The microstructure, surface morphology and leakage mechanisms of BNT and LCMO/BNT composite films were revealed by X-ray diffraction, scanning electron microscopy and semiconductor device analyzer, respectively. Ferroelectric behavior along with a remnant polarization (2P_r) of 20 μC/cm², saturated magnetization around 56 emu/cm³ and magnetoelectric effect (ME) voltage coefficient α_ME of 33 mV/cm Oe at 1 kHz for LCMO/BNT composite films were obtained at room temperature, indicating that the coupling effects of electric and magnetic field exist in the fabricated LCMO/BNT multiferroic composite thin films. And our observations provide an effective way to manipulate the conduction behavior and push forward understanding the leakage mechanism in LCMO/BNT composite films.     

X-ray-induced persistent photoconductivity in La0.9A0.1MnO3 (A=Sr, Ca)

We observed persistent photoconductivity (PPC) in La-based perovskite manganese oxides, La_0.9Sr_0.1MnO₃ (LSMO) and La_0.9Ca_0.1MnO₃ (LCMO), under X-ray irradiation. The PPC in LSMO was attributed to the collapse of the charge- and orbital-ordered (CO and OO, respectively) states, similar to that reported in previous papers. This PPC effect was different from that observed in a similar compound with a slightly different composition. This difference was explained in terms of doped carriers. This observation of PPC in LCMO is the first result of the PPC in a compound in which the ground state is not the CO phase; it was attributed to the collapse of the OO ground state. We proposed that OO ground state is a prerequisite for the occurrence of PPC in these compounds.     

Preparation of La0.67Ca0.33MnO3:Ag x polycrystalline by sol–gel method

La_0.67Ca_0.33MnO₃:mol%Ag _x (LCMO:Ag _x , x = 0, 0.04, 0.08, 0.10 and 0.20) ceramics were prepared by sol–gel method. The X-ray diffraction studies of the LCMO:Ag _x samples confirm the pure phase of the LCMO composites with Pbnm space group. With the increase of Ag doping from x = 0 to 0.20, the normalized resistivity (ρ/ρ _300K ) of the samples around the metal–insulator transition temperature (T _p ) reduced in sequence. Both T _p and the peak of temperature coefficient of resistance (T _k ) improved 5–8 K. Energy dispersive X-ray spectroscopy analysis showed that the composition of La, Ca and Mn of the obtained LCMO composites was in accordance with the composition of the precursor. The results indicated that the improvement of grain boundaries and crystallization were responsible for the enhancements of ρ, T _p and T _k of LCMO:Ag _x composites. The fitted curves of electrical resistivity for LCMO:Ag _x composites indicated that the mechanisms of grain/domain boundary, electron–electron and magnon scattering and adiabatic small polaron hopping are proposed to explain the phase transition of ferro-magnetic metallic region (T < T _p ) and the para-magnetic insulating region (T > T _p ), respectively.