Ferroelectric Property and Crystal Structure of KNbO3 Based Ceramics

Rietveld refinement analysis was carried out to obtain the knowledge on the solid solution structure of the La and Fe co-doped KNbO₃ ceramics. The diffraction data was well fitted with tetragonal space group P4mm, and showed that La and Fe located at K and Nb sites in KNbO₃ perovskite, respectively. The sum of both occupancy ratios agreed almost well with the doping content. Furthermore, the effects of MnO₂ addition on the ferroelectric properties and crystal structure of the La and Fe co-doped KNbO₃ ceramics were investigated. MnO₂ addition strongly affected the ferroelectric and piezoelectric properties, because the valence of Mn ions changed from Mn^{4 +} to some extents of Mn^{3 +} and Mn²⁺, which were suggested by XAFS analysis.     

Defect Chemistry of Y Doped BaTiO3

Defect chemistry of Y doped BaTiO₃ was investigated as a function of the Ba/Ti ratio. When the Ba/Ti ratio was greater than unity, Y^{3 +} was substituted for the normal Ti site and the equilibrium conductivity showed a strong evidence of acceptor-doped behavior. With the Ba/Ti ratio < 1, Y^{3 +} was substituted for the Ba site and the equilibrium conductivity showed donor-doped behavior. In the case excess Y₂O₃ was added to the stoichiometric BaTiO₃(Ba/Ti = 1), the conductivity profile showed a donor-doped behavior at low concentrations (< 1.0 mol%), whereas, at higher donor levels (> 2.0 mol%), the equilibrium conductivity minimum shifted toward lower Po₂, indicating acceptor doped behavior.     

Donor-Acceptor Charge Complex Formation in Barium Titanate Ceramics: Role of Firing Atmosphere

BaTiO₃ ceramics containing Mn acceptors and various Mo, W and Nb donor dopants have been fired in reducing atmosphere and re-oxidized in N₂/O₂. In single Mn-doped ceramics, Mn²⁺ is completely oxidized to Mn³⁺; in N₂ containing 50 ppm O₂ at T > 800°C. Changes of the Curie point and sample length under reduction and re-oxidation have been detected using dielectric and thermomechanical measurements. Charge compensation and complex formation between acceptors and donors have been observed. In donor-acceptor charge complexes, Mn²⁺ cannot be oxidized.     

Effect of Cr additions on the microstructural stability of Ni electrodes in ultra-thin BaTiO3 multilayer capacitors

Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the stability of ultra-thin Ni electrodes in BaTiO₃-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for 5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point (Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO₃ interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase mass-transfer along the Ni-BaTiO₃ interfaces facilitating an acceleration of Ni electrodes discontinuities.     

Effect of Cr2O3 addition on the microstructure and electrical properties of Mn-Ni-Co oxides NTC thermistors

The as-sintered Mn_1.1Ni_1.4Co_0.5O₄ crystallized in the solid solution of cubic spinel Mn-Ni-Co oxides, along with a small amount of the cubic spinel Ni-rich oxide phase. On the other hand, the Cr-substituted Mn_1.1Ni_1.4 Co_{0.5− x} Cr _x O₄ (0.07 ≤x ≤q 0.35) showed a single phase of cubic spinel Mn-Ni-Co-Cr oxides. This indicates that the substituted Cr suppressed the decomposition in the oxides. In addition, the Cr hindered the grain growth during sintering and increased the porosity. The electrical resistivity, the B _25/85 constant, and the activation energy of the Mn_1.1Ni_1.4Co_{0.5− x} Cr _x O₄ NTC thermistors increased with increasing Cr content. It is demonstrated that the Cr-substituted Mn_1.1Ni_1.4Co_{0.5− x} Cr _x O₄ NTC thermistors provided a variety of electrical properties, depending on the composition.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

Dysprosium Doped Dielectric Materials for Sintering in Reducing Atmospheres

Substitution of Dy rare earth ions was studied in Ba(Ti,Zr)O₃ dielectric materials, using thermogravimetry, X-ray diffraction and dielectric measurements. Dy³⁺ ions enter both the A- and the B-sites of the perovskite structure, however, the solubility on B-sites is up to 9 mol %, whereas it is only 2.5 mol% on A-sites. Dy can be easily shifted from A- to B-sites and back, using Ba or Ti excess in the material. Dy³⁺ on B-sites is a strong electron acceptor. Dy doped dielectric materials are cofired with Ni electrodes in reducing atmosphere to highly insulating BME multilayer capacitors.     

Preparation and characterization of LiNi0.80Co0.20– x Al x O2 as cathode materials for lithium ion batteries

LiNi_0.80Co_{0.20− x} Al _x O₂ samples (x = 0.025, 0.050 and 0.100) were prepared by a solid-state reaction at 725^∘C for 24 h from LiOH⋅H₂O, Ni₂O₃, Co₂O₃ and Al(OH)₃ under oxygen flow. LiNiO₂ simultaneously doped by Co-Al has been tried to improve the cathode performance. The results showed that substitution of optimum amount Al and Co at the Ni-site in LiNiO₂ improved cycling performance. As a consequence, LiNi_0.80Co_0.15Al_0.05O₂ has 178.2 mAh/g of the first discharge capacity and 174.0 mAh/g after 10 cycles. Differential capacity vs. voltage curves indicated that the Co-Al co-doped LiNiO₂ showed suppression of the phase transitions compared with pure LiNiO₂.     

Kinetics of (Fe,Cr)7C3/Fe dense ceramic layer prepared by in situ synthesis

Abstract

In this study, the (Fe,Cr)₇C₃/Fe dense ceramic layer was produced by in situ synthesis method with subsequent heat treatment. According to the results of thermal analysis, the as-cast specimen was subjected to heat treatment at 1186, 1208, 1230?°C for 1–5?h in argon atmosphere respectively. The microstructures of the compound region were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the kinetics of the (Fe,Cr)₇C₃ dense ceramic layer were analyzed. The results show that a-Fe and (Fe,Cr)₇C₃ are the predominant crystalline phases in the composite obtained. Depending on the layer process time and temperature, the thickness of the reaction layer formed on the substrate ranged from 12.3 to 32.6?mm. The kinetics of dense ceramic layer by the in situ synthesis method was also studied and the activation energy for the diffusion process was estimated to be 292?kJ/mol. Moreover, an attempt was made to investigate the possibility of predicting the iso-thickness of chromium carbide layer variation and to establish some empirical relationships between process parameters and dense ceramic layer thickness.     

Dielectric properties and schottky barriers in silver tantalate-niobate thin film capacitors

Abstract

Submicron thick ferroelectric Ag(Ta,Nb)O₃ films have been pulsed laser deposited on the bulk Pt₈₀lr₂₀ polycrystalline substrates. They are ferroelectric at temperatures below 125 K with the remnant polarization of 0.4 μC/cm² @ 77K and paraelectric at higher temperatures with tanδ@ 100 kHz as low as 0.015. Extensive I-V characterization has been performed in a wide temperature range 77 K to 350 K for vertical Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitive cells, where the metals Me = Pd, Au, Cr, and Al have been used as a top electrode. The electronic transport in thin Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitors follows the Schottky emission mechanism with the barrier height for the Pd, Au, Cr, and Al of 0.85, 0.8, 0.74, and 0.69 eV, respectively.     

Effect of Cr additions on the electrical properties of Ni–BaTiO3 ultra-thin multilayer capacitors

Multilayer ceramic capacitors based on BaTiO₃ dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the continuity of ultra-thin Ni electrodes in Ni–BaTiO₃ multilayer capacitors could be achieved. Here, the effect of the Cr addition to the nickel electrode pastes is studied with regard to the electrical properties. Low-field electrical measurements demonstrate no major differences between Cr doped Ni and undoped Ni. However, high-field measurements show a significant decrease to the total capacitor resistance. Under a critical electrical bias the conductivity significantly increases due to a Fowler–Nordheim tunneling conduction though the interfacial Schottky barrier at the dielectric–electrode interface; the onset voltage of this conduction is much lower than with the undoped nickel. Based on these results, we evaluate criteria for the selection of an appropriate refractory metal in order to improve the Ni electrode continuity.     

Based on the Study on Preparation and Properties of Co(II) and La3+-Doped TiO2 Electrochromic Film

Abstract

In order to improve the optical properties and coloration effect. Co(II) and La³⁺ doped TiO₂ thin films were synthesized via a sol–gel, by using butyl titanate as precursor on the surface of ITO conductive glass substrate. Several techniques were used to characterize produces. Adopting the Sol-gel technology, [CH₃(CH₂)₃O]₄Ti, La₂O₃, CoC_l2?6H₂O as the precursor, the composite membranes with different molar ratio of Ti, Ti/La, Ti/Co to be prepared on the ITO glass substrate, the optimum technological parameters for preparation of the base material of the electro-induced discoloration glass are determined. The structure and surface morphology optical and electrochromic properties of Co(II) and La³⁺-doped TiO₂ films were examined with X-ray diffraction (XRD) analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometer (UV-vis) DTA-TG analysis. It was found that:

1. The sintering temperature coating number, [CH₃(CH₂)₃O]₄Ti content of the TiO₂ film sample, and the doping category are the main factors that affect the structure and properties of the membrane based material;

2. Using two alcohol amine as chelating agent can effectively inhibit the formation of Ti (OH)₄ precipitation;

3. The properties of the TiO₂ glass film prepared by La₂O₃ and CoCl₂·6H₂O are fine;

4. Materials based on the preparation of a radiochromic film transmittance, high cyclic reversibility, cyclic voltammetry characteristics significantly, the results of the study for the electric induced radiochromic film-based material development and application provide a theoretical and experimental basis.

     

Partial Electronic Conductivity and Chemical Diffusivity of Li<Subscript>3<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>2/3−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> Solid Solution

Partial electronic conductivity and chemical diffusivity of Li have been measured on the system of Li_3xLa_2/3–xTiO₃ (LLT) with x = 0.13, a prospective Li⁺ electrolyte, against oxygen activity in the range of 10^–22 < a_O2 < 0.21 at 557, 610 and 663C, respectively by an ion-blocking polarization technique. It is found that the electronic conductivity of LLT, which in air is essentially an ionic conductor, varies as a_O2^–1/4 to render it mixed-conductive in reducing atmospheres, say, in a_O2 < 10^–12. The chemical diffusivity of component Li also increases from a value of the order of 10^–8 cm²/s in air atmosphere up to a maximum on the order of 10^–3 cm²/s as the electronic conductivity increases with decreasing oxygen activity. This is attributed to the variation of the electronic transference number and the thermodynamic factor with oxygen activity. The latter has been evaluated to be on the order of 10–10³.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Electrical properties of Ga2O3-based dielectric thin films prepared by plasma enhanced atomic layer deposition (PEALD)

Ga₂O₃ and Ga₂O₃-TiO₂ (GTO) nano-mixed thin films were prepared by plasma enhanced atomic layer deposition with an alternating supply of reactant sources, [(CH₃)₂GaNH₂]₃, Ti(N(CH₃)₂)₄ and oxygen plasma. The uniform and smooth Ga₂O₃ and GTO thin films were successfully deposited. Excellent step coverage of these films was obtained by chemisorbed chemical reactions with oxygen plasma on the surface. The dielectric constant of GTO thin film definitely increased compared to Ga₂O₃ film, and the leakage currents of GTO films were comparable to Ga₂O₃ films. The leakage current density of a 40-nm-GTO film annealed at 600^∘C was approximately 1×10⁻⁷ A/cm² up to about 600 kV/cm.     

SOL-GEL PREPARATION AND CHARACTERIZATION OF MULTIFERROIC BiFeO3 THIN FILMS WITH VARIOUS BI/FE RATIO

ABSTRACT

BiFeO₃ thin films have been prepared on Pt/TiO₂/SiO₂/Si substrates by sol-gel method using precursor solutions of various elemental ratio (Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1). The θ < eqid2 > 2θ scan XRD patterns show all the films consist mainly of polycrystalline perovskite and the crystallinity of Bi:Fe = 1.1:1.0 is better than the others. SEM and AFM images show all BiFeO₃ film have rosette structures, which consist of perovskite phase and matrix phase. The leakage current density measured at the temperature of 80 K is lower than 10^?4 A/cm² in all the films when the electric field reaches 1.6 MV/cm. The leakage mechanism of BiFeO₃ thin film is dominated by Schottky conduction at 80 K. At 80 K, the remanent polarizations at maximum applied voltage of 2.8 MV/cm are 100, 49, and 44 μC/cm² for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. The saturated magnetization of BiFeO₃ thin films at 80 K were found to be 14, 22.5, 15 emu/cm³ for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. Among these ratio, BiFeO₃ thin film deposited from precursor of Bi:Fe = 1. 1:1.0 gives the best ferroelectric property.     

(Zr/Ti) ratio effect on RF magnetron sputtered lead titanate zirconate films

Abstract

Sputtered Pb(Zr_xTi_1?x)O₃ thin films with various (Zr/Ti) compositions ranging from 15/85 to 70/30 were grown and characterised in terms of structural and electrical properties. PZT thin films, with 0.7–0.8μm thickness, were deposited on Si/SiO₂/Ti/Pt by sputtering followed by conventional annealing. The sputtering conditions were the same for all the compositions. There were no apparent differences in crystallographic orientation as a function of Zr/Ti and the films a-lattice constant evolution is not exactly identical to the one of bulk ceramics. The permittivity increases when the Zr concentration increases and decreases just after the mor-photropic composition i.e. Zr-rich films. The ferroelectric properties are very sensitive to the Zr/Ti ratio. For example, the coercive field increases when the Ti concentration in the film increases.     

Influences of Fe Element on the Structural and Electrochemical Performances of LiNi0.5Co0.2Mn0.3O2 Cathode Materials

The effect of Fe element on the structural and electrochemical performance of the Layered LiNi_0.5Co_0.2Mn_0.3O₂ materials with various Fe-doped amounts synthesized by high-temperature solid state method had been studied quantitatively and in detail. The structural and morphological of the prepared samples were characterized by X-ray diffraction patterns (XRD) and scanning electron microscopy (SEM). The study results show that the discharge capacity and cycling performance of the LiNi_0.5Co_0.2Mn_0.3O₂ all reduced by Fe doping, that is mainly attributed to the aggravated disorder degree of the layered structure and charge transfer resistance. Fe content should be controlled strictly in the layered LiNi_1?x?yCo_xMn_yO₂ cathode materials production process.     

The influence of lithium content in xLi[Li1/3Mn2/3]O2 · (1-x)Li[NiaCobMn(1-a+b)]O2 cathode materials prepared by co-precipitation method

The Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode system with various compositions of excess lithium in the range of x?=?1.3?~?1.9 was added to Li_x(Ni_aCo_bMn_(1-a+b))O₂ cathode materials synthesized using the co-precipitation method to investigate its microstructure and electrochemical properties. The X-ray diffraction (XRD) patterns of the prepared powders showed a hexagonal α–NaFeO₂ structure (space group: R-3 m, 166) and the existence of Li₂MnO₃ phase in the composite structure. The morphology of the prepared powders consisted of spherical agglomerates with particle size varying from 5 to 8 μm. The size increased with increasing Li content. The observed discharge capacity for the Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode (x?=?1.3, 1.5, 1.7, 1.9) for the first cycle was 46, 126, 206, and 94 mAhg^-1 for Li_1.7(Ni_aCo_bMn_(1-a+b))O₂, respectively_.     

The Dopant Distribution in Ti-, Zr- and Cr-doped Y3Al5O12 Fibers Grown by the Laser Heated Floating Zone Method

Single crystal fibers of Ti-, Zr- and Cr-doped Y₃Al₅O₁₂ (YAG) were grown from polycrystalline feed rods in Ar+5%H₂, pure Ar and Ar+2%O₂ atmospheres using the laser heated floating zone method. The spatial dopant distribution and precipitation of second phases in the grown fibers has been systematically studied by means of electron probe microanalysis. A strong growth-atmosphere dependence of effective segregation coefficient and precipitate formation were seen in Ti- and Cr-doped fibers, but not in Zr-doped fibers. The highest doping of Ti into the YAG lattice was obtained in Ar+5%H₂ atmosphere, while Cr was able to be incorporated into YAG by suppression of evaporation under an Ar+2%O₂ atmosphere. The results are discussed in terms of atmosphere-dependent valence state and volatility of the dopant.