Synthesis and investigations on the stability of La0.8Sr0.2CuO2.4+δ at high temperatures

For application in solid oxide fuel cells La_0.8Sr_0.2CuO_2.4+δ was synthesized and the phase evolution was characterized after quenching from different temperatures and after slow cooling. A single phase perovskite was found after quenching from 950 °C. The electrical conductivity of the La_0.8Sr_0.2CuO_2.4+δ perovskite exhibited metallic behavior reaching values of about 270 S/cm at 800 °C in air. The thermal expansion between 30 and 800 °C gave a thermal expansion coefficient of 11.1 × 10^− 6 K^− 1.At higher temperatures, the perovskite was transformed to the K₂NiF₄-type structure via an intermediate stage that can be best described as a LaSrCuO₄ phase with preferential growing of {020} lattice planes. After sintering at 1100 °C and slow cooling in the furnace a phase mixture of (La,Sr)CuO_4+δ and (La,Sr)CuO_2.4+δ perovskite was obtained. This phase mixture showed higher electrical conductivity (400 S/cm at 800 °C) and smaller thermal expansion coefficient (9.6 × 10^− 6 K^− 1) than the single phase La_0.8Sr_0.2CuO_2.4+δ perovskite.     

In situ characterization of transport properties of superconducting (Cu, C)-system thin films

Transport properties of (Cu, C)Ba₂CuO_x [(Cu, C)-1201] thin films have been characterized by in situ temperature dependence of resistivity, without breaking vacuum from the deposition to the measurement. In in situ transport properties measurements, the obtained results reveal that (Cu, C)Ba₂CuO_x films exhibit T_c > 20 K on the cased of conductivity at 290 K (σ_[290 K]) > 4 × 10² S/cm and temperature coefficient of resistivity (TCR) > 1.5 × 10^?3 K^?1, and doping level of them should be in between under-doped and optimally-doped states. Their results suggest that there would be possible to further increases of T_c, and XPS data suggest that (Cu, C)-system should have the excellent dopability in their charge reservoir and the possibility of low anisotropy.     

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R₀A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 10⁴ Ω/cm², and the average value of R₀A was 1.66 × 10⁴ Ω/cm². The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.     

Dielectric relaxation of CsHSeO4 above room temperature

Dielectric measurements of CsHSeO₄ show a distinct relaxation at low frequencies at several isotherms (T < 363 K). For example, the relaxation frequency is around 4 kHz at 323 K and increases to higher frequencies (~ 100 kHz) as the temperature increases. The relaxation has an activation energy of 0.8 eV, which is in close agreement with that associated with transport of charge carriers. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SeO₄^? 2 reorientation that cause distortion and change the local lattice polarizability, inducing dipoles like HSeO₄^?.     

Superconductivity in bulk T′-(La,Sm)2CuO4 prepared via a molten alkaline hydroxide route

We have synthesized La_2?xSm_xCuO₄ (0 ? x ? 2.0) with the Nd₂CuO₄ structure via a molten alkaline hydroxide route at temperatures as low as 400–480 °C. After reduction heat treatment in vacuum at 600–750 °C for removal of excess oxygen atoms at the interstitial apical site, superconductivity with T_c = 20–24 K was observed in the samples with x = 0.05–1.0. The superconducting volume fraction is nearly 100% for x = 0.3–0.7. Our results demonstrate that La_2?xSm_xCuO₄ with no nominal carrier doping is a bulk superconductor.     

Internal evaluation of impregnation treatment of waterlogged wood; relation between concentration of internal materials and relaxation time using magnetic resonance imaging

The purpose of this study is to clarify the degree of impregnation resulting from treatment of internal waterlogged wood samples using MRI. On a 1.5 T MR scanner, T₁ and T₂ measurements were performed using inversion recovery and spin-echo sequences, respectively. The samples were cut waterlogged pieces of wood treated with various impregnation techniques which were divided into different concentrations of trehalose (C₁₂H₂₂O₁₁) and polyethylene glycol (PEG; HO-(C₂H₄O)_n-H) solutions. Then these samples underwent impregnation treatment every two weeks. From the results, we found that the slope of the T₁-concentration curve using linear fitting showed the value of the internal area for PEG to be higher than the external area; internal, − 2.73 ms/wt% (R² = 0.880); external, − 1.50 ms/wt% (R² = 0.887). Furthermore, the slope of the T₁-concentration curve using linear fitting showed the values for trehalose to have almost no difference when comparing the internal and the external areas; internal, − 2.79 ms/wt% (R² = 0.759); external, − 3.02 ms/wt% (R² = 0.795). However, the slope of the T₂-concentration curve using linear fitting for PEG showed that there was only a slight change between the internal and the external areas; internal, 0.26 ms/wt% (R² = 0.642); external, 0.18 ms/wt% (R² = 0.920). The slope of the T₂-concentration curve did not show a change in linear relationship between the internal and the external areas; internal, 0.06 ms/wt% (R² = 0.175); external, − 0.14 ms/wt% (R² = 0.043). In conclusion, using visualization of relaxation time T₁, it is possible to obtain more detail information noninvasively concerning the state of impregnation treatment of internal waterlogged wood.     

Dielectric relaxation in NH4HSO4 above room temperature

The dispersion curves of the dielectric response of NH₄HSO₄ show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 10⁵ Hz at 31 °C, which shifts to higher frequencies (∼ 10⁶ Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy E_a = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SO₄⁻ reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO₄⁻.     

Densely mapping the phase diagram of cuprate superconductors using a spatial composition spread approach

A novel spatial composition spread approach was used successfully to deposit a 52-member library of La_2?xSr_xCuO₄ (0 ? x ? 0.18) using magnetron sputtering combined with physical masking techniques. Two homemade targets of La₂CuO₄ and La_1.82Sr_0.18CuO₄ were sputtered at a power of 41 W RF and 42 W DC, respectively, in a process gas of 15 mTorr argon. The libraries were sputtered onto LaSrAlO₄ (0 0 1), SrTiO₃ (1 0 0) and MgO (1 0 0) substrates through a 52-slot shadow mask for which a ?20 V substrate bias was applied to prevent resputtering. The resulting amorphous films were post-annealed (800 °C for 1 h then at 950 °C for 2 h) in a tube sealed with oxygen gas. Wavelength Dispersive Spectroscopy (WDS) analysis revealed the expected linear variation of Sr content from 0 to 0.18 with an approximate change of 0.003 per library member. Transport measurements revealed superconducting transitions as well as changes in the quasiparticle scattering rate. These transitions and scattering rate changes were mapped to produce the T-hole concentration phase diagram.     

Hole superconductivity in Nd2 − zCezCuO4

The reclassification of Nd_2 − zCe_zCuO₄from an electron superconductor to a hole superconductor is suggested by simple valence and electrostatics arguments: In Nd_2 − zCe_zCuO₄, isolated Ce substituting for Nd is not an electron donor; the proposed actual dopant is a defect-complex of Ce and interstitial oxygen which provides holes, making Nd_2 − zCe_zCuO₄a hole superconductor.     

Low-temperature synthesis of T′-La2CuO4 using CaH2 as reductant

We have successfully synthesized polycrystalline bulk samples of La₂CuO₄ with the Nd₂CuO₄-type (T′) structure at low temperatures. First of all, La₂CuO₄ with the K₂NiF₄-type (T) structure was prepared by the conventional solid-state reaction. Secondly, La₂CuO_3.5+δ with the Sr₂CuO₃-type structure was obtained by heating mixed powder of T-La₂CuO₄ and CaH₂ at 175 °C in an evacuated Pyrex tube. Thirdly, T′-La₂CuO_4+δ was prepared by heating La₂CuO_3.5+δ at 250 °C in air. Finally, T′-La₂CuO_4+δ was reduced using CaH₂ to remove excess oxygen. The powder X-ray diffraction pattern has revealed that the product is of the single phase of T′-La₂CuO₄, but no superconductivity has been observed at T > 2 K in the magnetic susceptibility measurement. The residual excess oxygen may suppress the appearance of superconductivity.     

Finite size effect and influence of temperature on electrical properties of nanocrystalline Ni–Cd ferrites

Electrical conductivity and dielectric measurements have been investigated for four different average grain sizes ranging from 3 to 7 nm of nanocrystalline Ni_0.2Cd_0.3Fe_2.5−xAl_xO₄ (0.0 ⩽ x ⩽ 0.5) ferrites. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of the Al doped Ni–Cd ferrites. The analysis of data shows only one semi-circle corresponding to the grain boundary volume suggesting that the conduction mechanism takes place predominantly through grain boundary volume in the studied samples. The variation of impedance properties with temperature and composition has been studied in the frequency range of 120 Hz–5 MHz between the temperatures 300–473 K. The hopping of electrons between Fe³⁺ and Fe²⁺ as well as hole hopping between Ni³⁺ and Ni²⁺ ions at octahedral sites are found to be responsible for conduction mechanism. The dielectric constant and loss tangent (tan δ) are found to decrease with increasing frequency, whereas they increase with increasing temperature. The dielectric constant shows an anomalous behavior at selected frequencies, while the temperature increases, which is expected due to the generation of more electrons and holes as the temperature increases. The behavior has been explained in the light of Rezlescu model.     

Interfacial reactions of Ba2YCu3O6+z with coated conductor buffer layer,LaMnO3

Chemical interactions between the Ba₂YCu₃O_6+x superconductor and the LaMnO₃ buffer layers employed in coated conductors have been investigated experimentally by determining the phases formed in the Ba₂YCu₃O_6+x–LaMnO₃ system. The Ba₂YCu₃O_6+x–LaMnO₃ join within the BaO–(Y₂O₃–La₂O₃)–MnO₂–CuO_x multi-component system is non-binary. At 810 °C (p_O2 = 100 Pa) and at 950 °C in purified air, four phases are consistently present along the join, namely, Ba_2?x(La_1+x?yY_y)Cu₃O_6+z, Ba(Y_2?xLa_x)CuO₅, (La_1?xY_x)MnO₃, (La,Y)Mn₂O₅. The crystal chemistry and crystallography of Ba(Y_2?xLa_x)CuO₅ and (La_1?xY_x)Mn₂O₅ were studied using the X-ray Rietveld refinement technique. The Y-rich and La-rich solid solution limits for Ba(Y_2?xLa_x)CuO₅ are Ba(Y_1.8La_0.2)CuO₅ and Ba(Y_0.1La_1.9)CuO₅, respectively. The structure of Ba(Y_1.8La_0.2)CuO₅ is Pnma (No. 62), a = 12.2161(5) Å, b = 5.6690(2) Å, c = 7.1468(3) Å, V = 494.94(4) Å³, and D_x = 6.29 g cm^?3. YMn₂O₅ and LaMn₂O₅ do not form solid solution at 810 °C (p_O2 = 100 Pa) or at 950 °C (in air). The structure of YMn₂O₅ was confirmed to be Pbam (No. 55), a = 7.27832(14) Å, b = 8.46707(14) Å, c = 5.66495(10) Å, and V = 349.108(14) Å³. A reference X-ray pattern was prepared for YMn₂O₅.     

Silver-coated LiVPO4F composite with improved electrochemical performance as cathode material for lithium-ion batteries

Nano-structured LiVPO₄F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO₄F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO₄F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO₄F material exhibits high discharge capacity, good cycle performance (108.5 mAh g⁻¹ after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g⁻¹ for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (R_ct) of LiVPO₄F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO₄F for lithium-ion batteries cathode material.     

Studies of structural and electrical properties on four-layers Aurivillius phase BaBi4Ti4O15

BaBi₄Ti₄O₁₅ (BBT) ceramic was synthesized using mixed oxide route and the structural and electrical properties were investigated systematically. The structural studies confirmed it to be an n=4 member of the Aurivillius oxide. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel–Fulcher relation wherein f₀=8.37E+14 Hz, E_a=0.13 eV, and T_f=608.18 K. The diffuseness parameter γ established the relaxor nature and it was attributed to the A-site cationic disorder. The specimen exhibited the excellent reproducibility in the measurements of displacement current, a remnant polarization of 5.4 μC/cm², and a coercive field of 4.03 MV/m. The room temperature piezoelectric coefficient d₃₃ was found to be 23 pC/N and the field-induced strain S was about 0.018% at the 8 MV/m electric field.     

Coexistence of magnetism and superconductivity in R1.4Ce0.6RuSr2Cu2O10 − δ(R = Eu,Sm and Gd)

The superconducting R_1.4Ce_0.6RuSr₂Cu₂O_10 − δ(R = Sm, Eu and Gd) withT_c ∼ 28, 32 and 42 K are also magnetically ordered atT_N ∼ 220, 122 and 180 K, respectively, thus,T_N ⪢ T_c. This is in contrast to intermetallic magnetic superconductors (such as RNi₂B₂C) in whichT_c ⪢  T_N. Magnetic susceptibility and Mossbauer spectroscopy show that superconductivity is confined to the CuO₂planes, whereas magnetism is due to the Ru sublattice. Irreversibility phenomena and magnetic anomalies, observed at low magnetic fields originate from antisymmetric exchange coupling of the Dzyaloshinsky–Moria type, and from spin reorientation of the Ru moments. The shielding fraction is about 100%, supporting the conclusion that the materials consist of a single phase, manifesting both magnetism and superconductivity at once.     

Fabrication of type-II InAs/GaSb superlattice long-wavelength infrared focal plane arrays

In this paper, we present an InAs/GaSb type-II superlattice (SL) with the M-structure for the fabrication of a long-wavelength (10 μm range) infrared (LWIR) focal plane arrays (FPA), which are grown by molecular beam epitaxy (MBE). The M-structure is named for the shape of the band alignment while the AlSb layer is inserted into the GaSb layer of InAs/GaSb SL. A 320 × 256 LWIR FPA has been fabricated with low surface leakage and high R₀A product of FPA pixels by using anodic sulfide and SiO₂ physical passivation. Experiment results show that the devices passivated with anodic sulfide obviously have higher R₀A than the un-sulphurized one. The 50% cutoff wavelength of the LWIR FPA is 9.1 μm, and the R₀A is 224 Ω cm² with the average detectivity of 2.3 × 10¹⁰ cm Hz^1/2 W⁻¹.     

Structure and relaxor behavior of BaBi4Ti4−xZrxO15 ceramics

BaBi₄Ti_4−xZr_xO₁₅ with x = 0.1, 0.2, 0.3 and 0.5, has been synthesized via modified solid state reaction route. X-ray diffraction studies confirmed the formation of single phase Zr⁴⁺ substituted BaBi₄Ti₄O₁₅ up to x = 0.2. ZrO₂ and Bi₂O₃ based impurity phases were found at x = 0.3 and 0.5 substitutions. However, Rietveld refinement showed the increase in lattice parameters of BaBi₄Ti₄O₁₅ up to x = 0.5 substitutions. A broad dielectric peak associated with frequency dependence dielectric maximum temperature was observed at low substitutions. Relaxor behavior was suppressed at x = 0.5 substitution. A broadening and shifting of permittivity-temperature peak was found for the substitution. The high temperature slopes of dielectric peaks were analyzed by quadratic law for relaxors. The degree of relaxation and phase transformation diffusiveness were investigated at different substitutions.     

A comparative study of the Ruddlesden-Popper series,Lan+1NinO3n+1 (n = 1, 2 and 3), for solid-oxide fuel-cell cathode applications

A comparative investigation of the much-studied La₂NiO_4+δ (n = 1) phase and the higher-order Ruddlesden-Popper phases, La_n+1Ni_nO_3n+1 (n = 2 and 3), has been undertaken to determine their suitability as cathodes for intermediate-temperature solid-oxide fuel cells. As n is increased, a structural phase transition is observed from tetragonal I4/mmm in the hyperstoichiometric La₂NiO_4.15 (n = 1) to orthorhombic Fmmm in the oxygen-deficient phases, La₃Ni₂O_6.95 (n = 2) and La₄Ni₃O_9.78 (n = 3). High temperature d.c. electrical conductivity measurements reveal a dramatic increase in overall values from n = 1, 2 to 3 with metallic behavior observed for La₄Ni₃O_9.78. Impedance spectroscopy measurements on symmetrical cells with La_0.9Sr_0.10Ga_0.80Mg_0.20O_3−δ (LSGM-9182) as the electrolyte show a systematic improvement in the electrode performance from La₂NiO_4.15 to La₄Ni₃O_9.78 with ∼ 1 Ω cm² observed at 1073 K for the latter. Long-term thermal stability tests show no impurity formation when La₃Ni₂O_6.95 and La₄Ni₃O_9.78 are heated at 1123 K for 2 weeks in air, in contrast to previously reported data for La₂NiO_4.15. The relative thermal expansion coefficients of La₃Ni₂O_6.95 and La₄Ni₃O_9.78 were found to be similar at ∼ 13.2 × 10^− 6 K^− 1 from 348 K to 1173 K in air compared to 13.8 × 10^− 6 K^− 1 for La₂NiO_4.15. Taken together, these observations suggest favourable use for the n = 2 and 3 phases as cathodes in intermediate-temperature solid-oxide fuel cells when compared to the much-studied La₂NiO_4+δ (n = 1) phase.     

Crystal growth and characterization of a new co-ordination complex—barium tetrakis(maleate) dihydrate

Crystals of barium tetrakis(maleate) dihydrate [Ba₄(C₄H₂O₄)₄]^?2H₂O are grown in gelated hydrosilica matrix. Single crystal X-ray diffraction studies show that the crystal system is monoclinic with space group P2₁/c. The unit cell dimensions are a=9.3721(2)  Å, b=20.5880(7)  Å, c=14.0744(4) Å, α=γ=90°, β=90.289(2)°. Powder XRD studies confirmed the single phase nature of the grown crystals. The FTIR data is in conformity with the XRD results. The TG–DTA curves of the material indicate a three-step thermal decomposition. The response of the dielectric properties in the temperature range 30 °C to 500 °C is correlated with the TG–DTA results.     

Enhanced ionization of perpendicularly aligned H2 in intense laser fields

Using three-dimensional classical ensembles, we have investigated the enhancement of double ionization of perpendicularly aligned H₂ molecules by a 800 nm laser pulse with intensity ranging from 1 × 10¹⁴ W/cm² to 6 × 10¹⁴ W/cm². The simulated results show that double ionization probability of H₂ strongly depends on R and reaches a maximum at an intensity independent critical distance R_C ≈ 5 a.u. Furthermore, the enhancement of double ionization is more pronounced in the cases of weaker or stronger fields. These results, a well indication of the influence of molecular structures and laser–molecule interactions on double ionization of diatomic molecules, are analyzed in detail and qualitatively explained based on the field-induced barrier suppression model and back analysis.