Effect of annealing atmosphere on the structural and electrical properties of BiFeO3 multiferroic ceramics prepared by sol–gel and spark plasma sintering techniques

Phase-pure BiFeO₃ powders were synthesized by sol–gel technique. Based on these powders, high-density BiFeO₃ ceramics were prepared by spark plasma sintering (SPS) at 700 °C along with annealing for 2 and 4 h, respectively, at 650 °C under atmospheres of air and oxygen. X-ray diffraction analysis revealed that the 4 h-oxygen-annealed sample contained a single rhombohedral perovskite phase while the samples annealed in the other conditions contained small quantities of impurity phases besides the rhombohedral perovskite phase. The relative density of the 4 h-oxygen-annealed sample was about 96%, being apparently higher than that of the other samples. In comparison with the 4 h-air-annealed sample, the dielectric constant of the 4 h-oxygen-annealed sample was relatively higher. The activation energy for electrical conduction was about 1.17 eV for the 4 h-oxygen-annealed sample while it was about 0.98 eV for the 4 h-air-annealed sample, showing that the former would have a lower room-temperature conductivity (~2.6×10⁻¹⁴ S cm⁻¹) than the latter (~2.1×10⁻¹³ S cm⁻¹). It is therefore anticipated that the oxygen-annealed sample could possess better ferroelectric properties as compared to the air-annealed sample.     

Deposition of highly oriented lanthanum nickel oxide thin film on silicon wafer by CSD

This paper describes the orientation control and the electrical properties of the chemical solution deposition (CSD) derived LaNiO₃ (LNO) thin film. The LNO precursor solutions were prepared using lanthanum nitrate and nickel acetate as La and Ni source, and ethanol or 2-methoxyethanol and 2-aminoethanol mixed solution as solvents. The LNO films were spin-coated using these precursor solutions and annealed at the temperature from 500 to 700 °C. The resulting LNO film annealed at 700 °C derived from 2-methoxyethanol and 2-aminoethanol mixed solvent exhibited (1 0 0)-orientation, with some surface cracks and pores, and relatively higher resistivity of 2.49 × 10⁻³ Ω cm. The LNO film derived from 2-methoxyethanol and 2-aminoethanol mixed solvent annealed at 700 °C in an oxygen atmosphere showed highly (1 0 0)-orientation, with higher density, a few cracks and pores, and exhibited a good electrical resistivity of 7.27 × 10⁻⁴ Ω cm.     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Ion implantation and anneal to produce low resistance metal–diamond contacts

Contacts to boron-doped, (100)-oriented diamond implanted with Si or with Si and B were formed and the effects of dose, implantation energy and anneal treatment on the specific contact resistance were examined. Ti/Au contacts on heavily implanted diamond (10¹⁶ Si ions cm⁻², E_i=30 keV or 10¹⁷ Si and B ions cm⁻², E_i=15 keV (Si) and E_i=10 keV (B)) had a specific contact resistance lower than the best contacts produced on unimplanted diamond. A specific contact resistance of (1.4±6.4)×10⁻⁷ Ω cm⁻² was achieved following a 450°C anneal. The results were consistent with a reduction in barrier height brought about by silicide formation. Light silicon implantation (10¹³ ions cm⁻²) or relatively light dual implantation (B, Si<10¹⁶ ions cm⁻²) did not reduce the specific contact resistance. Increasing the diamond conductivity by 4×10⁴ decreased the specific contact resistance by over three orders of magnitude, in agreement with the trend observed by Prins (J.F. Prins, J. Phys. D 22 (1989) 1562).     

Formation of a heavily B doped diamond layer using an ion implantation technique

In this report, we present a study on lattice and electronic structures of B doped layers formed using B implantation into diamond. Boron layers were produced using the multiple-energy B ion implantation (total dose: 2.1 × 10¹⁵ to 1.7 × 10¹⁷ cm^− 2) into type IIa diamond at ~ 400 °C. Optical absorption and Hall effects were measured in the range of 80−1000 K for investigating the change of the lattice and electronic structures with the B concentration in diamond. The p-type carrier conduction was observed at 80−1000 K in all the samples. While a lightly B doped sample displays typical semiconductive, temperature-dependent valence-band conduction, heavily B doped samples have the very weak or almost zero temperature dependence of the carrier concentrations, resistivity and Hall mobility in this temperature region, suggesting characteristics of a p-type degenerate semiconductor. In such heavily doped samples, broad optical absorption bands, most likely corresponding to Drude absorption originating from free holes, were observed. The minimum resistivity and the sheet resistance at room temperature among the samples were 1.4 mΩcm and 56 Ω/□, respectively. These results indicate that very low-resistive p-type degenerate semiconducting layers were produced, preserving diamond lattice (preventing graphitization), despite high-dose ion irradiation.     

Silicon carbide films from polycarbosilane and their usage as buffer layers for diamond deposition

Thin films of polycarbosilane (PCS) were coated on a Si (100) wafer and converted to silicon carbide (SiC) by pyrolyzing them between 800 and 1150 °C. Granular SiC films were derived between 900 and 1100 °C whereas smooth SiC films were developed at 800 and 1150 °C. Enhancement of diamond nucleation was exhibited on the Si (100) wafer with the smooth SiC layer generated at 1150 °C, and a nucleation density of 2 × 10¹¹ cm^− 2 was obtained. Nucleation density reduced to 3 × 10¹⁰ cm^− 2 when a bias voltage of − 100 V was applied on the SiC-coated Si substrate. A uniform diamond film with random orientations was deposited to the PCS-derived SiC layer. Selective growth of diamond film on top of the SiC buffer layer was demonstrated.     

Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.     

Pd ohmic contacts to p-SiC 4H, 6H and 15R polytypes

A new metallization process at sample temperatures up to 600°C during deposition of the metals is employed for producing low resistivity narrow Pd ohmic contacts to p-SiC epitaxial layers of 4H, 6H and 15R polytypes. It is found that the values of the specific contact resistances were equal for the same Na–Nd concentration in all investigated polytypes. On epitaxial layers with Na–Nd=4×10¹⁸ cm⁻³ a specific contact resistance of 4×10⁻⁴ Ω cm² has been measured. Electrical and structural features of these contacts were investigated.     

The effect of calcium on the properties of SmBa1−xCaxCoCuO5+δ as a cathode material for intermediate-temperature solid oxide fuel cells

The effect of calcium on the properties of SmBa_1–xCa_xCoCuO_5+δ (x = 0.0–0.3) as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is evaluated systematically. Samples exhibit a highly crystalline double perovskite phase, and their cell volumes decrease as x is changed from 0.0 to 0.3. The oxygen content and average thermal expansion coefficient (TEC) of SmBa_1–xCa_xCoCuO_5+δ decreases as the calcium content increased. An average TEC of as low as 15.3 × 10⁻⁶ °C⁻¹ is obtained for SmBa_0.7Ca_0.3CoCuO_5+δ. The area specific resistances at 700 °C decrease by approximately 50% when the calcium content is increased from x = 0.0 (0.173 Ω cm²) to x = 0.3 (0.086 Ω cm²). The maximum power densities of SmBa_1−xCa_xCoCuO_5+δ-based single cells at 800 °C increase from 635 mW cm⁻² (x = 0.0) to 939 mW cm⁻² (x = 0.3).     

Heavy phosphorus doping by epitaxial growth on the (111) diamond surface

Semiconducting n-type diamond can be fabricated using phosphorus as a substitutional donor dopant. The dopant activation energy level at 0.58 eV is deep. At high dopant concentrations of 10²⁰ cm^− 3 the activation energy reduces to less than 0.05 eV. Phosphorus doping at concentrations of 10²⁰ cm^− 3 or higher has been achieved with epitaxial growth on the (111) diamond crystallographic surface. In this work epitaxial growth of diamond with high phosphorus concentrations exceeding 10²⁰ cm^− 3 is performed using a microwave plasma-assisted chemical vapor deposition process with process conditions that include a pressure of 160 Torr. This pressure is higher than previous phosphorus doping reports of (111) surface diamond growth. The other growth conditions include a feedgas mixture of 0.25% methane and 500 ppm phosphine in hydrogen, and a substrate temperature of 950–1000 °C. The measured growth rate was 1.25 μm/h. The room temperature resistivity of the heavily phosphorus doped diamond was 120–150 Ω-cm and the activation energy was 0.027 eV.     

Diamond based field-effect transistors with SiNx and ZrO2 double dielectric layers

A diamond-based field-effect transistor (FET) with SiN_x and ZrO₂ double dielectric layer has been demonstrated. The SiN_x and ZrO₂ gate dielectric are deposited by plasma-enhanced chemical vapor deposition (PECVD) and radio frequency (RF) sputter methods, respectively. SiN_x layer is found to have the ability to preserve the conduction channel at the surface of hydrogen-terminated diamond film. The leakage current density (J) of SiN_x/ZrO₂ diamond metal-insulator-semiconductor FET (MISFET) keeps lower than 3.88 × 10^− 5 A·cm^− 2 when the gate bias was changed from 2 V to − 8 V. The double dielectric layer FET operates in a p-type depletion mode, whose maximum drain-source current, threshold voltage, maximum transconductance, effective mobility and sheet hole density are determined to be − 28.5 mA·mm^− 1, 2.2 V, 4.53 mS·mm^− 1, 38.9 cm²·V^− 1·s^− 1, and 2.14 × 10¹³ cm^− 2, respectively.     

Influence of post-annealing atmosphere on microstructure,optical and electrical properties of zinc cadmium oxide films deposited by DC and RF magnetron co-sputtering

Zinc cadmium oxide (Zn_1−xCd_xO) films were deposited on quartz substrates by direct current (DC) and radio frequency (RF) reactive magnetron co-sputtering and the influence of post-annealing atmosphere on their microstructure, optical and electrical properties were investigated by X-ray diffraction (XRD), optical absorbance, photoluminescence (PL) and Hall measurements. Results indicate that the band gap (E_g) of all Zn_1−xCd_xO films annealed in different atmospheres are smaller than that of the undoped ZnO, the observed shifts in E_g being 0.43, 0.37 and 0.32 eV for the Zn_1−xCd_xO films annealed in argon, oxygen and vacuum, respectively. Hall measurement results indicate that all Zn_1−xCd_xO films annealed in different atmospheres show the n-type conduction, but the Zn_1−xCd_xO film annealed in vacuum has low resistivity and high concentration, which has room-temperature resistivity of 1.59 Ω cm and carrier concentration of 2.07×10¹⁷ cm⁻³. Compared with Zn_1−xCd_xO films annealed in oxygen and argon, Zn_1−xCd_xO film annealed in vacuum has the best crystal quality, luminescence and electrical properties. The influencing mechanism of the post-annealing atmosphere on the electrical and optical properties of the Zn_1−xCd_xO film is discussed.     

Neutron transmutation of 10B doped diamond

Free standing ¹⁰B isotope doped diamond films deposited by chemical vapor deposition in a microwave chamber were irradiated to thermal neutron fluence values of 0.32 × 10¹⁹, 0.65 × 10¹⁹, 1.3 × 10¹⁹, and 2.6 × 10¹⁹ n/cm². Cooling of the diamond films was maintained during irradiation. In a separate experiment, neutron irradiation to a total fluence of 2.4 × 10²⁰ n/cm² with equal fast and thermal neutrons was also performed on a diamond epilayer without cooling during irradiation. The formation of defects in the diamond films was characterized using Raman, FTIR, photoluminescence, electron paramagnetic resonance spectroscopy, and X-ray diffraction. It was found that defect configurations in diamond responsible for an increase in continuum background in the one-phonon region of Raman spectrum were absent in the films that have been cooled. The FTIR peak at 1530 cm^− 1 annealed in the sample irradiated to a fluence of 2.6 × 10¹⁹ n/cm² indicating that the sample reached a temperature of 300 °C during irradiation. Absence of characteristic infrared absorption peaks that were observed only upon annealing neutron irradiated diamond is used to conclude that the temperature of the sample during neutron irradiation to a fluence of 2.6 × 10¹⁹ n/cm² was well below 650 °C needed for mobility of defects and accumulation of stable unrecoverable damage. On the other hand, results from diamond epilayer subjected to equal thermal and fast neutron fluence of 2.4 × 10²⁰ n/cm² and without cooling showed that defects formed from displaced carbon atoms became mobile and formed complex configurations of irrecoverable damage. Electrical conductance of the unirradiated and irradiated diamond samples was measured as a function of temperature to determine the compensation of the p-type by the n-type charge carriers.     

Ionic conductivity of Mn2+ doped dense tin pyrophosphate electrolytes synthesized by a new co-precipitation method

Mn²⁺-doped Sn_1−xMn_xP₂O₇ (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at <150 °C. The dopant Mn²⁺ acts as a sintering aid and leads to dense Sn_1−xMn_xP₂O₇ samples on sintering at 1100 °C. Though conductivity of Sn_1−xMn_xP₂O₇ samples in the ambient atmosphere is 10⁻⁹–10⁻⁶ S cm⁻¹ in 300–550 °C range, it increases significantly in humidified (water vapor pressure, pH₂O = 0.12 atm) atmosphere and reaches >10⁻³ S cm⁻¹ in 100–200 °C range. The maximum conductivity is shown by Sn_0.88Mn_0.12P₂O₇ with 9.79 × 10⁻⁶ S cm⁻¹ at 550 °C in ambient air and 2.29 × 10⁻³ S cm⁻¹ at 190 °C in humidified air. It is observed that the humidification of Sn_1−xMn_xP₂O₇ samples is a slow process and its rate increases at higher temperature. The stability of Sn_1−xMn_xP₂O₇ samples is analyzed.     

Manganese-rich SmBaCo2−x−yMnxMgyO5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) with stable structure and low thermal expansion coefficient as cathode materials for IT-SOFCs

SmBaCo_2−x−yMn_xMg_yO_5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) samples are synthesized by sol-gel method. The influence of different substitution of Mn and Mg for Co on crystal structures, thermal expansion coefficient (TEC), electrical conductivities and electrochemical performances have been investigated. The generation of the secondary phase BaMnO₃ is suppressed with Mg²⁺ increasing. Demonstrated by temperature-dependent X-ray diffraction from 25 °C to 700 °C, the structure of SmBaCo_0.4Mn_1.5Mg_0.1O_5+δ in high temperature is stable. The TEC of SmBaCo_1.45Mn_0.5Mg_0.05O_5+δ, SmBaCo_0.95MnMg_0.05O_5+δ, SmBaCo_0.45Mn_1.5Mg_0.05O_5+δ and SmBaCo_0.4Mn_1.5Mg_0.1O_5+δ are 15.77 × 10⁻⁶ K⁻¹, 16.20 × 10⁻⁶ K⁻¹, 12.19 × 10⁻⁶ K⁻¹ and 12.58 × 10⁻⁶ K⁻¹, respectively, which are much lower than those of cobalt-based layered perovskites and more compatible with the thermal expansion of SDC electrolyte. Although the electrochemical performances of SmBaCo_2−x−yMn_xMg_yO_5+δ (x = 0.5, 1, 1.5 and y = 0.05, 0.1) decrease slightly with Mn increasing, the polarization resistances of the SmBaCo_1.45Mn_0.5Mg_0.05O_5+δ and SmBaCo_0.4Mn_1.5Mg_0.1O_5+δ are 0.17 Ω cm² and 0.30 Ω cm² at 800 °C, respectively, which can meet the electrochemical performance requirements of cathode materials. Among the samples, the SmBaCo_1.45Mn_0.5Mg_0.05O_5+δ and SmBaCo_0.4Mn_1.5Mg_0.1O_5+δ show better tradeoff properties between TEC and electrochemical performance as cathode materials for IT-SOFCs.     

Synthesis of high-quality AZO polycrystalline films via target bias radio frequency magnetron sputtering

The deposition rate, transmittance and resistivity of aluminium-doped zinc oxide (AZO) films deposited via radio frequency (r.f.) sputtering change with target thickness. An effective method to control and maintain AZO film properties was developed. The strategy only involved the regulation of target bias voltage of r.f. magnetron sputtering system. The target bias voltage considerably influenced AZO film resistivity. The resistivity of the as-deposited AZO film was 9.82×10⁻⁴ Ω cm with power density of 2.19 W/cm² at target self-bias of −72 V. However, it decreased to 5.98×10⁻⁴ Ω cm when the target bias voltage was increased to −112 V by applying d.c. voltage. Both growth rate and optical band gap of AZO film increased with the absolute value of target bias voltage – growth rate increased from 10.54 nm/min to 25.14 nm/min, and band gap increased from 3.57eV to 3.71 eV when target bias voltage increased from −72 V to −112 V at r.f. power density of 2.19 W/cm². The morphology of AZO films was slightly affected by the target bias voltage. Regulating target bias voltage is an effective method to obtain high-quality AZO thin films deposited via r.f. magnetron sputtering. It is also a good choice to maintain the quality of AZO film in uptime manufacturing deposition.     

Rapid oxidative activation of carbon nanotube yarn and sheet by a radio frequency,atmospheric pressure,helium and oxygen plasma

Carbon nanotube yarn and sheet were activated using radio frequency, atmospheric pressure, helium and oxygen plasmas. The nanotubes were exposed to the plasma afterglow, which contained 8.0 × 10¹⁶ cm⁻³ ground state O atoms, 8.0 × 10¹⁶ cm⁻³ metastable O₂ (¹Δ_g), and 1.0 × 10¹⁶ cm⁻³ ozone. X-ray photoelectron spectroscopy and infrared spectroscopy revealed that 30 s of plasma treatment converted 25.2% of the carbon atoms on the CNT surface to oxidized species, producing 17.0% alcohols, 5.9% carbonyls, and 2.3% carboxylic acids. The electrical resistivity increased linearly with the extent of oxidation of the CNT from 4 to 9 × 10⁻⁶ Ω m. On the other hand, the tensile strength of the yarn was decreased by only 27% following plasma oxidation.     

Characterization of spray pyrolytically deposited high mobility praseodymium doped CdO thin films

Praseodymium (Pr) doped CdO thin films with high transparency and high mobility were deposited, using a homemade spray pyrolysis setup, on micro-slide glass substrates preheated at 300 °C. Polycrystalline nature and Cd-O bond vibration of deposited films were confirmed by X-ray diffraction, micro-Raman and Fourier transform infrared spectroscopy analyses. The oxidation state of Cd²⁺, O²⁻, and Pr³⁺ was confirmed by X-ray photoelectron spectroscopy analysis. The highest average particle size (92 nm-FESEM) and high RMS (13.48 nm-AFM) values are obtained for 0.50 wt% Pr doped CdO thin film. The optical band gap is varied between 2.38 eV and 2.52 eV, depending on the Pr doping concentration. Photoluminescence spectra revealed that Pr doped CdO thin film exhibits strong green emission at 582 nm. High mobility (82 cm²/V s), high charge carrier concentration (2.19×10²⁰ cm⁻³) and high transmittance (83%) were observed for 0.50 wt% Pr doped CdO film. A high figure of merit (9.79×10⁻³ Ω⁻¹) was obtained for 0.50 wt% Pr doped CdO thin films. The mechanism behind the above results is discussed in detail in this paper.     

Mechanistic study of ion-induced diamond nucleation

The effect of low-energy ion bombardment of silicon on diamond nucleation was investigated. By bombarding 100 eV ions of methane and hydrogen on a silicon substrate prior to diamond growth by chemical vapor deposition, diamond nucleation can be immensely enhanced. The ion beam treatment deposited a layer of nano-crystalline graphitic carbon embedded with amorphous SiC. Diamond then nucleated on the graphite overlayer; the nucleation density increased with increasing ion dose. At 1×10¹⁹ ions cm⁻², a nuclei density of 4×10⁸ cm⁻² was obtained. These results show that ion bombardment of the substrate enhances diamond nucleation.     

Ce0.9Gd0.1O1.95 supported La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for solid oxide fuel cells

Lanthanum-based iron- and cobalt-containing perovskite has a high potential as a cathode material because of its high electro-catalytic activity at a relatively low operating temperature in solid oxide fuel cells (SOFCs) (600–800). To enhance the electro-catalytic reduction of oxidants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF), Ga doped ceria (Ce_0.9Gd_0.1O_1.95, GDC) supported LSCF (15LSCF/GDC) is successfully fabricated using an impregnation method with a ratio of 15 wt% LSCF and 85 wt% GDC. The cathodic polarization resistances of 15LSCF/GDC are 0.015 Ω cm², 0.03 Ω cm², 0.11 Ω cm², and 0.37 Ω cm² at 800 °C, 750 °C, 700 °C, and 650 °C, respectively. The simply mixed composite cathode with LSCF and GDC of the same compositions shows 0.05 Ω cm², 0.2 Ω cm², 0.56 Ω cm², and 1.20 Ω cm² at 800 °C, 750 °C, 700 °C, and 650 °C, respectively. The fuel cell performance of the SOFC with 15LSCF/GDC shows maximum power densities of 1.45 W cm^?2, 1.2 W cm^?2, and 0.8 W cm^?2 at 780 °C, 730 °C, and 680 °C, respectively. GDC supported LSCF (15LSCF/GDC) shows a higher fuel cell performance with small compositions of LSCF due to the extension of triple phase boundaries and effective building of an electronic path.