Griffiths Phase and Reduced Magnetization of La0.5Ca0.5MnO3 with Different Annealing Temperature

In this paper, the existence of Griffiths phase and variation of ferromagnetism have been studied for La_0.5Ca_0.5MnO₃ nanoparticles annealed at different temperatures. It is detected by x-ray diffraction patterns that the increasing of annealing temperature induces the increment of grain size. The magnetization as a function of temperature demonstrates that magnitude of magnetization at low temperature is decreased as the annealing temperature increases, which is explained by the core-shell model. The temperature dependence of inverse susceptibility of those samples manifests that the Griffiths phase occurs for the samples annealed at temperatures 900?°C and 1150?°C and it disappears for the sample annealed at 1350?°C. The reduction of Griffiths phase with increasing of annealing temperature indicates the suppression of quenched disorder after annealing, which may be related to the lower degree of disorder, redistribution of magnetic ions, and weaker hybridization of?O?2p states with its near-neighbor atoms. As to the disappearance of Griffiths phase, competition between paramagnetic, ferromagnetic, and antiferromagnetic phases plays a very important role.     

Effect of rapid thermal annealing on Zn/ZnO layers

Zn/ZnO layers were deposited on SiO₂/Si substrate by magnetron sputtering at room temperature, and then these layers were annealed at various temperatures from 200 to 400 °C in nitrogen atmosphere for 1 min. The structural and electrical properties of the Zn/ZnO layers before and after annealing are systematically investigated by X-ray diffraction, scanning electron microscopy, current–voltage measurement system, and Auger electron spectroscopy. Current–voltage measurements show that the Zn/ZnO layers exhibit an Ohmic contact behavior. It is shown that, initially, the specific contact resistivity decreases with the increase of the annealing temperature and reaches a minimum value of 9.76 × 10^?5 Ω cm² at an annealing temperature of 300 °C. However, with a further increase of the annealing temperature, the Ohmic contact behavior degrades. This phenomenon can be explained by considering the diffusion of zinc interstitials and oxygen vacancies. It is also shown that Zn-rich ZnO thin films can be obtained by annealing Zn on the surface of ZnO film and that good Ohmic contact between Zn and ZnO layers can be observed when the annealing temperature was 300 °C.     

Size effect on magnetic and dielectric properties in nanocrystalline LaFeO3

Nanocystalline LaFeO₃ powders with different grain sizes (30–150 nm) have been synthesized by a polymerized complex method to investigate their magnetic and dielectric properties. Thermogravimetric–differential thermal analysis curves of the precursory powders reveal the thermal decomposition and crystallization temperature should be at above 650 °C. The precursory powders were sintered at temperatures of 650, 700, 800, and 900 °C for 2 h. X-ray diffraction identify that all the samples are phase-pure. Weak ferromagnetic behaviors and finite exchange bias (EB) effects were observed for all the samples at room temperature, and both M_r and H_EB decreases monotonically with the increase of grain size. For 30 nm sample, the remnant magnetization and the EB field are 0.086 emu/g and 310 Oe, respectively. On the other hand, the dielectric constants decrease with the decreasing of grain size. Among all the samples, 150 nm samples show the largest dielectric constant about 6 × 10³.     

Influence of annealing temperature on structural,electrical and optical properties of undoped zinc oxide thin films

The undoped zinc oxide thin films were grown on quartz substrate at a substrate temperature of 750 °C by radio frequency magnetron sputtering and post annealed at different temperatures (600–800 °C) for a period of 30 min. The influence of annealing temperature on the structure, electrical and optical properties of undoped ZnO thin films was investigated by X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the thin films were extremely sensitive to the annealing temperature and the conduction type could be changed dramatically from n-type to p-type, and finally changed to weak p-type when the temperature increased from 600 to 800 °C. Electrical and photoluminescence results indicate that native defects, such as oxygen and zinc vacancies, could play an important role in determining the conductivity of these nominally undoped ZnO thin films. The conversion of the conduction type was attributed to the competition between Zn vacancy acceptor and oxygen vacancy and interstitial Zn donors. At an intermediate annealing temperature of 750 °C, the film behaves the best p-type characteristic, which has the lowest resistivity of 12 Ωcm, hall mobility of 2.0 cm²/V s and carrier concentration of 1.5 × 10¹⁷ cm^?3. The photoluminescence results indicated that the Zn vacancy might be responsible for the intrinsic better p-type characteristic in ZnO thin films.     

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500?°C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400–2000?nm continuously increases as the annealing temperature increases from 500?°C to 700?°C, whilst it decreases first and then increases as the annealing temperature increases from 800?°C to 1000?°C. When the film is excited with a laser of 980?nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho³⁺: ⁵S₂/⁵F₄?→?⁵I₈?and ⁵F₅?→?⁵I₈ transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900?°C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.     

Effect of calcination temperature on structure and thermoelectric properties of CuAlO<Subscript>2</Subscript> powders

Copper aluminum oxide (CuAlO₂) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2H-CuAlO₂ and Al₂O₃ impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl₂O₄ (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E _g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K^?1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m^?1 K^?1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10^?8 to 4.94 × 10^?4 in the order of the literature reports. From the Arrhenius plot ln(σT) versus 1000/T, an activation energy E _a = 0.32 eV for the electrical conductivity was calculated.     

Phase transformation behavior of zinc metastannates obtained by aqueous precipitation at different temperatures

Phase transformation studies in ZnO–SnO₂ system from zinc metastannate (ZnSnO₃) to zinc orthostannate (Zn₂SnO₄) with annealing temperature are reported. Non-centrosymmetric oxides show unique symmetry dependent and spontaneous polarization properties, which are technologically important. ZnSnO₃ particles were synthesized by a simple aqueous synthesis at low temperatures designed with the assistance of potential–pH diagrams. ZnSnO₃ particles synthesized at 4 °C are more porous losing the ilmenite structure upon annealing at 200 °C, while the other samples prepared at higher temperatures (25–65 °C) becomes amorphous at 300 °C. The phase transformation into the inverse spinel orthostannate phase occurs around 750 °C in all the samples.     

The Influence of Annealing Temperature on the Magnetic Properties of Mn0.5Co0.5Fe2O4 Nanoferrites Synthesized via Mechanical Milling Method

Mn_0.5Co_0.5Fe₂O₄ nanosized ferrites have been made directly from MnFe₂O₄ and CoFe₂O₄ ferrites and from metal oxides by using high-energy ball milling. Single-phase formation and microstructure of the as-milled samples and samples annealed at 100, 200, 300, 400 and 500 ^°C under argon atmosphere were studied using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average grain sizes were estimated from XRD measurements and found to be between 7 and 11 nm. The microstrain for each sample was relieved by annealing due to crystallite growth. Room temperature magnetic properties were investigated by zero-field ⁵⁷Fe Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Saturation magnetizations of the samples were estimated using the empirical law of approach to saturation. The variation of coercive field, saturation magnetization, maximum magnetization and remanent magnetization for each sample was found to depend on the annealing temperature. The coercive fields are observed to increase with increased annealing temperature (from about 300 Oe for the as-milled samples to about 1000 Oe for samples annealed at 500 ^°C) which we attribute to increases in grain sizes.     

Zinc Ferrite Nanoparticles: New Preparation Method and Magnetic Properties

In this work, single phase zinc ferrite (ZnFe₂ O ₄) nanoparticles with a mean crystallite size of 12 nm were successfully prepared just by high energy wet milling of metallic Zn and Fe powders and water as the raw materials, without any subsequent heat treatments. Variation of the magnetization with respect to temperature was studied by Faraday balance. Room temperature M–H curve of the as-milled powder has an s-shape, which shows it has ferrimagnetic order. To investigate the effect of annealing on magnetic properties of the as-milled powder, it was annealed at different temperatures from 150 to 800 °C and characterized by XRD and magnetometry. The results show that cation distribution of the as-milled nanoparticles is different from that of the bulk zinc ferrite (normal spinel) and by annealing it changes drastically, and finally, it changes to that of the bulk one.     

Refinement of some basic features of Zr surface-layered Bi-2223 superconductor with diffusion annealing temperature

This study aims to investigate the influences of diffusion annealing temperatures on structural, morphological, electrical, and superconducting features of Zr surface-layered Bi-2223 ceramics. The present study also covers an in-depth understanding of correlations between disorders and transition temperatures. The Zr diffusion is carried out via an annealing process between 650 and 840 °C. The observed results depict that the Zr ions can easily diffuse into the deeper level of Bi-ceramics and possible Zr/Bi substitution has occurred due to the driving force of high thermal energy. Besides, it is found that the Zr diffusion improves the general crystallinity quantities of Bi-2223 ceramic up to 800 °C annealing temperature. In addition, better intergranular couplings with a smoother plate-like structure are extensively observed in surface morphology for the samples annealed at 800 °C. Significant refinements of both basic electrical resistivity, hole carrier densities, and critical temperatures with narrow transitions are also obtained for the Zr surface-layered Bi-2223 ceramics after the 800 °C annealing process. The obtained improvements in critical fundamental features can be attributed to the optimum pairing mechanism, best crystal structure quality, ideal Cu–O₂ interlayer coupling strengths, and enhanced interaction between adjacent superconductive layers. Besides, the first-order derivative of electrical resistivity versus temperature graphs indicates that the best annealing temperature enables to triggers to stabilize the superconductivity in the homogeneous regions. It can be concluded that the Zr impurity diffusion at 800 °C is promising for the improvement in the basic features of Bi-2223 superconducting systems for future applications in superconductor technology.

     

Einfluß einer Auslagerung unter Schutzgas bei 800 bis 1000 °C auf die mechanischen Eigenschaften des Werkstofftyps X 10 NiCrAlTi 32 20

Effects of Aging in Inert Gas at 800 to 1000 °C on the Mechanical Properties of X 10 NiCrAlTi32 20 Type Alloys Specimens of three casts of a X 10 NiCrAlTi32 20 type alloy with different carbon contents (0,04, 0,08 and 0,33 wt%) were annealed at 800, 900 and 1000°C between 6 and 900 h. Tensile- and notched bar impact-tests were performed at room temperature to characterize the changes of mechanical properties due to the heat treatments. The structural changes were recorded by optical metallography, scanning electron microscopy and transmission electron microscopy. The formation of fine dispersed M₂₃C₆-precipitates leads to hardening effects, which are lost by coarsening with longer annealing time or higher temperatures, where an embrittlement occurs. Only the low carbon version exhibits a dominant precipitation of Ti(C, N), especially at 1000°C, which maintains its ductility.     

Synthesis and Magnetic Properties of Barium Hexaferrite Powders Using Organic Acid Precursor Method

An investigation of the synthesis of BaFe₁₂O₁₉ powders by the organic acid precursor method is reported by acidic and neutral media. X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) are utilized to study the effect of organic precursor type and annealing temperature on the crystal structure, crystallite size, microstructure and magnetic properties of the formed powders. The XRD analysis showed that the crystalline BaFe₁₂O₁₉ phase was obtained at 1200 °C for 2 h using different carboxylic acids in acidic medium. However, pure BaFe₁₂O₁₉ was achieved at low annealing temperature 1000 °C in neutral medium. SEM micrographs showed that the particles were strongly influenced by type of carboxylic acid and the annealing temperature. VSM study indicated that the saturation magnetization was increased with increasing annealing temperature to 1200 °C as the result of formation of single barium hexaferrites phase. High saturation magnetization (M _s =66.5 emu/g) was achieved for the formed powders in neutral medium using tartaric acid as organic precursor. Wide coercivities of the formed powders (H _c =259–5114 Oe) were obtained.     

TiN as a high temperature diffusion barrier for arsenic and boron

The use of TiN thin films as high temperature diffusion barrier layers for arsenic and boron was investigated. The TiN films are formed by reactive evaporation at room temperature and then annealed at a higher temperature. TiN and TiN/TiSi₂ films are placed between heavily doped polycrystalline silicon films and single-crystal silicon substrates of opposite doping polarity for secondary ion mass spectrometry analysis and electrical measurements of Schottky and ohmic contacts respectively. The results indicate that TiN is a good diffusion barrier for arsenic at 900°C. The effectiveness of this property is degraded as the temperature exceeds 900°C and it becomes ineffective at 1000°C. TiN is a better diffusion barrier for boron than for arsenic. It allows limited diffusion of boron at temperatures of up to 1000°C. The TiN/TiSi₂ composite forms good ohmic contacts when the substrates are heavily doped. The ohmic contacts can survive after annealing at temperatures of up to 1000°C. It also forms good Schottky contacts when the substrates are lightly doped. The Schottky contacts can survive after annealing at temperatures of up to 950°C in one case and of up to 1000°C in another case.     

Synthesis and properties of magnetoresistive (La,Sr)MnO<Subscript>3</Subscript>-based glass-ceramic borate-matrix composites

Magnetic glass-ceramic borate-matrix composites containing micron-sized lanthanum strontium manganite grains have been prepared by ceramming amorphous La₂O₃-SrO-MnO _x -B₂O₃ materials at 800 and 900°C. The glass-ceramics had a magnetization of up to 48.7 A m²/kg in a magnetic field of 400 kA/m. Their relative magnetoresistance reached 6.2% at 290 K in a magnetic field of 80 kA/m and 16% at 77 K in a field of 160 kA/m.     

Effects of annealing and deposition temperature on the structural and optical properties of AZO thin films

Al-doped ZnO (AZO) thin films were deposited on p- type Si(100) substrate by r.f magnetron sputtering at 200, 300 and 400 °C substrate temperatures. The deposited films were annealed in air atmosphere for 1 h at temperatures of 700, 800 and 900 °C. The deposition temperature and post-deposition annealing effects on structural and optical properties of the AZO samples were analyzed using X-ray diffraction, atomic force microscope and photoluminescence (PL). After annealing, the value of full width half maximum of the diffraction peaks was decreased as well as, the intensity of visible and strong UV PL emission peaks were increased with temperature. However, the deep-level emission related with zinc point defects was removed by annealing of the samples. Results revealed that all of the as-deposited and annealed AZO films have hexagonal structure along (002) direction and their crystallinity were improved with the increased deposition and post-growth annealing temperatures. In addition, the surface roughness and the particle size of the films were increased with increased deposition and annealing temperatures.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Effects of growth temperature on electrical and structural properties of sputtered GaN films with a cermet target

GaN films have been deposited at 100–400 °C substrate temperature on Si (100) and sapphire (0001) substrates by RF reactive sputtering in an (Ar + N₂) atmosphere. A (Ga + GaN) cermet target for sputtering was made by hot pressing the mixed powders of metallic Ga and ceramic GaN. The effects of substrate temperature on the GaN formation and its properties were investigated. The diffraction results showed that GaN films with a preferential (10–10) growth plane had a wurtzite crystalline structure. GaN films became smoother at higher substrate temperature. The Hall effect measurements showed the electron concentration and mobility were 1.04 × 10¹⁸ cm^?3 and 7.1 cm² V^?1 s^?1, respectively, for GaN deposited at 400 °C. GaN films were tested for its thermal stability at 900 °C in the N₂ atmosphere. Electrical properties slightly degraded after annealing. The smaller bandgap of ~3.0 eV is explained in terms of intrinsic defects and lattice distortion.     

Epitaxial growth and annealing control of FMR properties of thick homogeneous Ga substituted yttrium iron garnet films

Homogeneous, 30 μm to 70 μm thick Ga substituted yttrium iron garnet films have been grown on Y or Al substituted gadolinium gallium garnet substrates having lattice parameters matched to that of the films. Resonance field and FMR linewidth measurements as a function of frequency and annealing experiments revealed that the magnetization and cubic anisotropy of the films are identical to data from flux grown bulk single crystals, the FMR losses of the films are only slightly higher. For films grown with supercooling ΔT < 50 °C a negative, growth induced, uniaxial anisotropy was found which could be removed by annealing in air at 1100 °C. A compensation of the temperature drift of the FMR frequency can be adjusted in the Ga substituted films by changing the frozen-in Ga-Fe cation distribution by annealing and quenching from different temperatures > 800 °C.     

Fine particles of lanthanum-and cobalt-doped strontium hexaferrite prepared through glass crystallization

Glass of nominal composition Sr_0.6La_0.4Fe_11.6Co_0.4O₁₉ + 12SrB₂O₄ was prepared by rapidly quenching an oxide melt and was then heat-treated at temperatures from 550 to 900°C to give glass-ceramics containing fine lanthanum-and cobalt-doped strontium hexaferrite particles and microcrystalline SrB₂O₄. The materials were characterized by x-ray diffraction, scanning electron microscopy, electron probe x-ray microanalysis, and magnetic measurements. The coercivity of the glass-ceramic samples was shown to increase up to 427 kA/m with increasing heat-treatment temperature. The saturation magnetization of the samples increases up to 25.0 A m²/kg as the heat-treatment temperature is raised to 750°C, and decreases slightly at higher temperatures. Dissolving the nonmagnetic matrix of the glass-ceramic prepared at 900°C, we obtained submicron powder of composition Sr_0.88La_0.12Fe_10.74Co_0.47O_y, as determined by x-ray microanalysis.     

Crystal orientation dependent microwave dielectric properties of sputtered SBTi thin films on fused silica substrates

Thin films of SBTi (SrBi₄Ti₄O₁₅) were deposited on fused silica substrates by rf-magnetron sputtering at substrate temperatures from 600 to 725 °C. The effect of substrate temperature on preferential orientation, microstructure, Raman scattering characteristics and microwave dielectric properties of SBTi thin films were investigated. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. As the substrate temperature increases, the preferential orientation changes from (119) to (0010). Films deposited at 700 °C exhibits less lattice distortion. It exhibits a dielectric constant about 110 and loss tangent about 0.06 at 10 GHz. It is seen from the Raman analysis that the films deposited at higher temperatures orients more towards c-axis which releases the torsional vibration mode involving TiO6 octahedra with a higher oscillator strength resulting in larger values of dielectric constant and dielectric loss for those films.