High-temperature ferromagnetic metallic phase in LaMnO3/Sr3Al2O6 heterostructure

To achieve a flexible single-crystal multifunctional membrane, the freestanding process of a rigid epitaxial transition metal oxide thin film via a buffered water-dissolution sacrificial layer has attracted reasonable attentions. Owing to the difference in chemical potential, specific element affinity, and lattice constant between the target membrane and the sacrificial layer, the freestanding process may cause an indelible change of physics property once the target thin film is sensitive to the...     

Impedance spectroscopy study of LaMnO3 modified BaTiO3 ceramics

Ba_0.97Ti_0.97La_0.02Mn_0.04O₃ nanocrystalline powder was prepared by chemical route with the help of soluble tartarate complex of Ti⁴⁺ ion. Preliminary X-ray diffraction analysis of crystal structure showed that a single-phase compound was formed exhibiting tetragonal system. Average crystallite size and particle size were observed to be between 27 and 33 nm, which were analyzed through XRD and transmission electron microscope respectively. Wide range impedance spectroscopy study from 200 to 600 °C showed the presence of both bulk and grain boundary effects up to 500 °C. The bulk conductivity indicated an Arrhenius-type thermally activated process and oxygen vacancies are the possible ionic charge carriers at higher temperatures. The variation of ac conductivity as a function of frequency indicated the possibility of hopping mechanism for electrical process in the system with a non-exponential type of conductivity relaxation.     

The effect of oxygen partial pressure on the properties of RF-sputtered Al2O3 thin films

Aluminum oxide thin films are used as insulating and passivating layers in a variety of microelectronic and other applications. RF bias sputtering was used to deposit Al₂O₃ films. The effects of oxygen partial pressure on the deposition rate, argon content, refractive index, etch rate, substrate temperature and uniformity were characterized by alpha-step scan, EDX, AES, XPS, STEM, X-ray diffraction and ellipsometry.     

Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure

Post-annealing of YBa₂Cu₃O₇ (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO₃ were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.     

Spin and orbital ordering in CaMnO3 and LaMnO3: UHF calculations and the Goodenough model

Relative energies from unrestricted Hartree–Fock (UHF) calculations for several spin and orbital orderings in CaMnO₃ and LaMnO₃ in cubic and tetragonally distorted perovskite structures are rationalised using the Goodenough model. Comparison of relative energies from several calculations leads to an estimate that the antiferromagnetic coupling energy exceeds the ferromagnetic coupling energy per Mn ion by 10 meV in both CaMnO₃ and LaMnO₃.     

Critical current density and microstructure of YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure

Post-annealing of thin films of YBa₂Cu₃O₇ (YBCO) has been performed at 29 Pa and 750°C. For films 0.6 m thick, a critical current density >1 MA cm^–2 is obtained at 77 K, with a sharp eddy current response at 25 MHz. Microstructural investigation of these films by crosssectional and planar transmission electron microscopy reveals that the YBCO film has thec-axis normal to the plane of the substrate in a continuous sheet of varying thickness, frequently covering the entire thickness of the film. Mutually perpendicular rods with thec-axis in the plane of the LaAlO₃ substrate are also seen. The microstructure and critical current density of these films are compared with those of previously reported films post-annealed in atmosphericpressure oxygen.     

Oxygen pressures over LaMnO3+x

Equilibrium oxygen partial pressures over non-stoichiometric lanthanum manganite, LaMnO_3+x, have been determined by a gravimetric method at 1188–1370 K. Relative partial molar free energy, entropy and enthalpy of solution of oxygen in this phase were derived. The variation of the relative partial molar entropy of oxygen with the composition in the non-stoichiometric LaMnO_3+x phase was calculated and discussed in relation to the metal vacancy model.     

Transition of sulfospinel to Th3P4 type phase under pressure

Sulfospinels AB₂S₄ (A=Mg, Mn, B=Tm, Yb) were treated at 1000°C and 55 kbar for 1h. The X-ray powder diffractions were completely indexed by assuming that the products were isostructural with Th₃P₄. The results of density measurements showed a good agreement with those calculated from the X-ray data. No magnetic ordering was observed in temperatures down to 77K.     

氧分压对反应磁控溅射ZrO2薄膜光学透射率的影响

从氧空位、表面粗糙度及晶界三方面,讨论了氧分压对射频反应磁控溅射ZrO2薄膜光学透射率的影响.结果表明,随氧分压增大,氧空位的减少使单斜相逐渐占优,缺氧状况的改善使薄膜透射率逐渐升高;高氧分压下,出现颗粒聚集现象,表面粗糙度大幅增加及晶粒的聚集长大,使薄膜透射率下降.     

Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure

The variation of critical current density at 77 K as a function of film thickness was studied for YBa₂Cu₃O₇ films on (100) LaAlO₃ substrates. Film thicknesses were in the range 0.2–1.6m. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm^–2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4m. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.     

The phase diagram YF3-GdF3

The binary phase diagram YF₃-GdF₃ was studied by differential scanning calorimetry (DSC). Yttrium fluoride and gadolinium fluoride show complete miscibility in all three phases (orthorhombic room temperature phase, trigonal or hexagonal high temperature phase, liquid). The transformations between room temperature and high temperature phases are of first order and occur at 1338.6 K (YF₃) or 1174.8 K (GdF₃). Melting points are 1403.1 K (YF₃) or 1525.7 K (GdF₃), respectively. The c_p(T) curve of GdF₃ shows a λ shaped local maximum at 1333 K that might be related to a further solid phase transformation of second order.     

Synthesis of three-dimensionally ordered porous perovskite type LaMnO3 for Al-air battery

LaMnO₃ catalysts with three-dimensionally ordered holes perovskite structure were prepared via close-packed SiO₂ template synthesized by Stöber-Frink method. SEM, XRD and BET were employed to characterize the microstructure, phases and specific surface area. CV method was used to the oxygen electrode behavior of catalysts. Diameter of the holes was about 330 nm, corresponding to the size of SiO₂ template. Full-cell discharge tests were performed on aluminum-air battery fabricated by porous LaMnO_3. Results showed that the discharge performance of porous LaMnO₃ were 1.54 V, 1.42 V and 1.24 V respectively when the discharge currents were set at 5 mA/cm², 10 mA/cm² and 20 mA/cm², respectively, which were higher than that of LaMnO₃ prepared by coprecipitation method (1.33 V, 1.09 V, 0.63 V, respectively).     

Fabrication of polycrystalline lanthanum manganite (LaMnO3) nanofibers by electrospinning

Lanthanum manganite (LaMnO₃) nanofibers were successfully fabricated by electrospinning utilizing sol-gel precursors. Polycrystalline cubic-perovskite structure LaMnO₃ fibers of 50-100 nm were obtained by calcination of the inorganic/organic hybrid fibers at 600 °C for 1 h. The XRD results showed that the grain size of the fibers increased significantly with the increase of calcinations temperature. The average diameter of crystal grains was 17 nm after calcined at 400 °C for 2 h, then grew to 20 nm after heated up to 600 °C for 1 h. The morphology, microstructure, crystal structure and thermal analysis were investigated by SEM, TEM, XRD and TG-DSC, respectively.     

Investigation of the effect of different oxygen partial pressure to LaAlO3 thin film properties and resistive switching characteristics

The pulsed laser deposition and growth of a high-k dielectric lanthanum aluminate LaAlO₃ (LAO) thin film on indium tin oxide/glass substrate at different oxygen partial pressure was studied. Based on the pulsed laser deposition growth mechanism, we explain how a difference in the oxygen partial pressure influences the surface roughness, formation of an interfacial layer, and the transparent resistive switching characteristics of LAO thin films. The micro-structure and oxygen concentration difference inside LAO thin films may be the main reason for the difference in electrical and resistive switching properties. Films grown at higher oxygen partial pressure displayed more reliable resistive switching performance, due to the formation of the interfacial layer and a lower concentration of oxygen vacancies. The interfacial layer serves as a good oxygen reservoir and the involvement of more oxygen ions ensures the switching reliability. The migration of oxygen ions between the interfacial layer and the LAO film under applied bias may be the switching mechanism.     

Microstructure and ferroelectric properties of epitaxial BaTiO3/SrRuO3/SrTiO3 (001) films grown by pulsed laser deposition under high oxygen pressure

BaTiO₃ films were epitaxially grown on SrTiO₃ (001) substrates buffered with SrRuO₃ films as bottom electrode by pulsed laser deposition under high oxygen pressure of 30 Pa. The quality of the BaTiO₃/SrRuO₃/SrTiO₃ multilayer films was analyzed by means of X-ray diffraction, atomic force microscopy and transmission electron microscopy. BaTiO₃ films were found to be highly c-axis-oriented tetragonal phase with c/a = 1.002. The dielectric constant first increased with increasing temperature, and showed a peak at the Curie temperature of about 356 K. The films had well-saturated hysteresis loops with a remnant polarization of 7.3 μC/cm² and a coercive field of 29.5 kV/cm at room temperature.     

Nonstoichiometric behavior and phase stability of rare earth manganites at 1200°C: (1). LaMnO3

The perovskite phase LaMnO_3±λ was revealed to have nonstoichiometry ranging from 2.947 to 3.079 under the oxygen partial pressure below logPO₂(atm)=0 at 1200°C. The presence of the reductive perovskite phase LaMnO_3?λ with a more distorted structure than the monoclinic one was ascertained. The free energy change of oxidative reaction in MnO+1/2La₂O₃+1/4O₂=LaMnO₃ was determined to be ΔG°=19500±200cal at 1200°C. D.C. electrical conductivities of LaMnO_3±λ perovskites at room temperature became higher with increasing oxygen content. Magnetic measurements were also made.     

Effects of periodicity and oxygen partial pressure on the crystallinity and dielectric property of artificial SrTiO3/BaTiO3 superlattices integrated on Si substrates by pulsed laser deposition method

Epitaxial SrTiO₃(STO)/BaTiO₃(BTO) artificial superlattices have been grown on TiN buffered Si (001) substrates by pulsed laser deposition method and the effects of stacking periodicity and processing oxygen partial pressure on their crystallinity and dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of STO/BTO superlattices were investigated using X-ray diffraction and transmission electron microscopy. The TiN buffer layer and superlattice thin films were grown with cube-on-cube epitaxial orientation relationship of [110](001)_films∣∣[110](001)_TiN∣∣[110](001)_Si. The c-axis lattice parameter of the STO/BTO superlattice decreased from 0.412 nm to 0.406 nm with increasing oxygen partial pressure and the dielectric constants, measured at the frequency of 100 kHz at room temperature, of the superlattices with 2 nm/2 nm periodicity increased from 312 at 1 × 10^− 5 Torr to 596 at 1 × 10^− 3 Torr. The dielectric constants of superlattices grown at oxygen partial pressure of 1 × 10^− 3 Torr increased from 264 to 678 with decreasing periodicity of the superlattices from 10 nm/10 nm to 1 nm/1 nm.     

AsNCa3 at high pressure

A constant pressure optimization scheme is applied to the study of ternary calcium nitrides under pressure. The enthalpy is minimized with respect to the electronic configuration, the positions of the atoms and the cell metric (i.e. the lattice parameters). Symmetry corrections can be performed during the relaxation towards the equilibrium structure in order to be able to investigate the compound in a certain proposed symmetry. We obtain excellent agreement with experiment for the zero-pressure structural parameters of the cubic anti-perovskite structure BiNCa₃ and of the distorted anti-perovskite structures AsNCa₃ and PNCa₃. For AsNCa₃ the structural parameters, band gap energies, etc. are investigated as a function of the pressure. A new cubic phase is predicted to have a lower enthalpy than the orthorhombic phase for pressures above 59 GPa.     

High pressure synthesis of Gd3InO6, Tb3InO6 and Lu3InO6

Three new compounds, X₃InO₆ (X = Gd, Tb, Lu) were prepared at 1–4 GPa, ～1050°C. They are monoclinic, space group $\text{P}\text{2}{}_1\text{n}$ with $\text{a}\text{? 8.9}\text{A}\text{?}$, $\text{b}\text{? 9.8}\text{A}\text{?}$, $\text{c}\text{? 5.9}\text{A}\text{?}$, β ～ 95° and Z = 4.     

Synthesis of alumina supported LaMnO3 with excellent thermal stability by a PVP-assisted route

LaMnO₃/Al₂O₃ catalysts were successfully prepared by a novel method with polyvinyl pyrrolidone (PVP) as complexant and characterized by XRD, TGA, IR, BET, XPS and TEM techniques. The TGA and IR characterizations of the precursor revealed that LaMnO₃ structure was formed under mild conditions without combustion of any organic compounds. The obtained catalysts exhibited better activity for methane combustion than those prepared by citrate method, mainly due to larger pore volume, more active oxygen species on surface and the formation of a pure perovskite structure. The high surface area of about 122 m² g⁻¹ was retained even after calcined at 1000 °C; and interestingly, no phase transformation or solid-state reaction was observed. This fact indicated the excellent thermal stability of catalysts, which was ascribed to the strong interaction between the support and active phase.