Decomposition behavior and dielectric properties of Ti-doped BiFeO3 ceramics derived from molten salt method

The effects of Ti-doping on the decomposition behavior, crystal structure, sintering behavior and dielectric properties have been investigated for the Ti-doped BiFeO₃ ceramics derived from molten salt method. XRD reveals the almost pure phase BiFeO₃ is synthesized in the Ti-doped BiFeO₃ powders. And the particle size of Ti-doped BiFeO₃ powers obviously decreases with the increase of Ti content. However, the sintering temperature elevates significantly after Ti-doping. The DC resistivity can enhance by up to four orders of magnitude (from 10⁴ to 10⁸?Ωm) with only 5 at% Ti doping. But the dielectric constant is suppressed from 10⁴ to 10², and dielectric loss obviously reduces with a small amount of Ti doping. The variation of dielectric properties has been discussed from the decomposition of BiFeO₃ phase. The Ti-doping can effectively suppress the decomposition reaction in Ti-doped BiFeO₃ ceramics.     

Optical and electric properties of strontium bismuth tantalate thin films

High quality SrBi₂Ta₂O₉ ferroelectric thin films were fabricated on platinized silicon using pulsed laser deposition. The optical properties of the thin films were studied by spectroscopic ellipsometry from the ultraviolet to the infrared region. Optical constants, n ∼ 0.25 in the infrared region and n ∼ 2.18 in the visible spectral region, were determined through multilayer analyses on their respective pseudodielectric functions. The band-gap energy is estimated to be 4.14 eV. It was found that the leakage current mechanism of the film was from bulk limited Poole-Frenkle emission to interface-controlled Schottky emission with applied field increasing, and that the breakdown field of the film had a negative linear variation with the logarithm of the electrode area.     

Effect of vanadium doping on sintering and dielectric properties of strontium barium niobate ceramics

Strontium barium niobate, Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics doping up to 3 wt% V₂O₅ were fabricated by solid state reaction route, starting from raw materials (oxides and carbonates) of analytical grade. The phase composition, microstructure and dielectric properties were investigated by X-ray diffraction, scanning electric microscope and impedance analyzer. The results show that the addition of V₂O₅ improves sintering densification of SBN ceramic samples. The relative density of the samples firstly increases and then slightly decreases with increasing amounts of V₂O₅ and sintering temperature. With the help of the additive of 1 wt% V₂O₅, the relative density of the sample sintered at 1,280 °C for 3 h can reached 97.2%. Only single tetragonal tungsten bronze phase SBN exists in all the doped samples. With increase in V₂O₅ content, the dielectric constant of SBN ceramics at both room temperature and in the vicinity of the phase transition temperature increases significantly and the Curie temperatures (Tc) obviously shifts to low temperature as well as the dielectric loss remains below 0.06. The diffuseness in the phase transition is found to increase with increase in vanadium doping level. The addition of V₂O₅ results in an increased grain size associated with rod-like grain growth.     

Effect of Al doping on structural and dielectric properties of PLZT ceramics

Polycrystalline samples of Al modified lead lanthanum zirconate titanate [PLZT] with Zr = 55% and Ti = 45%, have been synthesized by a high-temperature solid-state reaction technique. X-ray diffraction analysis of the compounds suggests the formation of a single-phase compound with tetragonal structure. Dielectric studies of the compounds as a function of temperature (from 30 to 350°C) at frequency (1, 10 and 100 kHz) show that the compounds undergo a phase transition of diffuse type.The transition temperature shifts towards higher side with increase in frequency a typical characteristic of a relaxor material. Diffusivity (γ) study of phase transition of these compounds provided its value between 1 and 2, indicating the variation of degree of disordering in the system. Measurement of dc resistivity (ρ) as a function of temperature (Room temperature, RT to 350°C) at a constant biasing field suggests the compounds have negative temperature coefficient of resistance (NTCR).     

Preparation, sintering, and microstructures of strontium barium bismuth tantalate layered perovskite ceramics

The solid solutions of Ba-doped SrBi₂Ta₂O₉ layered perovskite ceramic powders have been successfully prepared via a two-step process using BiTaO₄ as a precursor. The lattice constants of the solid solutions monotonically increase with increasing barium-ion content. The sinterability of (Sr_1–xBa_x)Bi₂Ta₂O₉ powders is significantly improved by increasing the barium-ion content. When the specimens with high barium-ion contents are sintered at 1100°C, they thermally decompose to form rod-like grains and the matrix expands, leading to a lower density. The addition of barium ions to SrBi₂Ta₂O₉ also results in significant variation in the morphology of the sintered specimens and the occurrence of c-axis preferred orientation which is ascribed to the anisotropic growth of plate-like grains. The precise control of the barium-ion content as well as the sintering conditions is critical for obtaining densified barium-ion doped SrBi₂Ta₂O₉ ceramics with a pure, layered perovskite structure.     

Piezoelectric and dielectric properties of PZT–PZN–PMS ceramics prepared by molten salt synthesis method

Piezoelectric powders and ceramics with the composition of Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Mn_1/3Sb_2/3)O₃ (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: _r = 1773; tan δ = 0.0040; T_c = 280 °C; d₃₃ = 455 pC/N; k_p = 0.70; Q_m = 888; E_c = 10.3 kV/cm; and P_r = 28.2 μC/cm², at calcination of 800 °C and sintering of 1120 °C temperature.     

Aging effects on dielectric properties of barium neodymium titanium tantalate ceramics

The aging effects on crystal structures and dielectric properties were investigated in Ba_pNd_6−pTi_8−pTa_2+pO₃₀ (p = 3, 4 and 5) ceramics with tungsten bronze structure. From XRD analyses on fresh and aged specimens, the slight change of crystal constant was concluded in Ba_pNd_6−pTi_8−pTa_2+pO₃₀ ceramics. Strong aging effects on the dielectric properties were observed in the present ceramics. After aging, a slightly decreased dielectric constant was observed combined with a significantly reduced dielectric loss in all the three compositions. These results had been discussed in term of the disorder-order state of ions at A- and B-sites. From tolerance factor and electronegativity difference, the stability was discussed for the filled type tungsten bronze phase.     

Preparation of fluoride-substituted hydroxyapatite by a molten salt synthesis route

Fluoride-substituted hydroxyapatite (FHAp) with high thermal and morphologic stability was successfully prepared by a molten salt synthesis route. XRD patterns and FTIR spectra identified the synthesized powders as FHAp solid solution. The FHAp obtained with potassium sulfate as the flux showed the rod-like morphology without detectable decomposition up to 1300°C and the flux, sodium sulfate, led to the spheriodal FHAp. After investigating the effects of salt species on the FHAp morphologies, it was found that solubility was not the exclusive factor, which affected the morphological development of apatite powders, and the cations of molten salt species also played an important role.     

铌酸锶钡陶瓷材料的制备及介电性能研究

以BaCO3，SrCO3和Nb205作为原料，采用高能球磨工艺制备SBN50陶瓷粉体。球磨后的粉体不经煅烧，直接压片成型，在1250～1350℃下保温1．5～12h可制备出SBN50陶瓷材料，并对此进行了X射线衍射分析、扫描电镜观察和性能测试。结果表明：球磨30h的粉体在1100℃时合成SBN50单相；随着烧结温度的升高和保温时间的延长，SBN50陶瓷的介电常数先增大后减小，晶粒大小呈有规律的变化。1300℃下保温3h制得的陶瓷样品介电常数最高（εmax=1447），居里温度（L）为130℃。     

锰掺杂对PMN-PZT陶瓷介电性能的影响

研究了锰掺杂对富锆PMN-PZT（铌镁酸铅一锆钛酸铅）陶瓷材料的相组成、微观结构、介电性能等方面的影响，并对实验结果作出物理机理的解释。实验结果表明：适量的锰掺杂有助于陶瓷晶粒的生长，并能有效地降低PMN-PZT陶瓷材料的介电常数和介电损耗，在锰掺杂量为3．0％（原子分数）时，εr：197、tanδ=0．15％，作为用于红外热释电探测器的陶瓷材料具有良好的介电性能。     

Lead-free ceramics based on alkaline niobate tantalate antimonate with excellent dielectric and piezoelectric properties

This paper reports lead-free (Na_0.52K_0.48−x)(Nb_0.94−xSb_0.06)O₃-xLiTaO₃ compositions with significantly enhanced piezoelectric properties. The 6% Sb substituted Na_0.52K_0.48NbO₃ was modified by a small amount of LiTaO₃, leading to the formation of a morphotropic phase boundary between orthorhombic and tetragonal phases in the range of x = 0.035-0.04 where the materials show a strong compositional dependence of various electrical properties. Excellent properties of d₃₃ = 335 pC/N, k_p = 53%, , Q_m = 41 and T_c = 291 °C were obtained in the composition with x = 0.04, indicating that the ceramics studied are promising as a lead-free piezoelectric candidate.     

Influence of samarium doping on the phase stability and optical properties of calcium silicates derived from agro-food wastes

Calcium silicates are very stable and good hosts for luminescent materials. These calcium silicates are synthesized using cost-effective agro-food wastes such as rice husk ash and eggshell powder along with doping of samarium oxide [Ca_3?xSi₂O₇:xSm³⁺(x(%)?=?0.25, 0.50, 0.75, and 1.00)] via solid-state reaction method. X-ray diffraction confirms that the Ca₃Si₂O₇ phase co-exists with the monoclinic-Ca₂SiO₄ phase. An increase in doping concentration of Sm³⁺ enhances the Ca₂SiO₄ phase content. Two types of morphology can be seen in the SEM micrographs confirming the presence of two phases. Photoluminescence emission spectra contain peaks in the visible region. Characteristic emission peaks of Sm³⁺ are present along with strong peaks due to the titanium ions present in agro-food wastes. Commission International de'Eclairage (CIE) co-ordinates correspond to the green region, which is significantly different from the CIE co-ordinates of Sm³⁺ doped samples derived from mineral oxides. This study presents an alternate use of agro-food wastes for synthesizing visible light-emitting phosphors and presents a mechanism for stabilizing Ca₂SiO₄ in waste-derived samples.

     

熔盐法制备铌镁酸铅基Y5V电子瓷料的研究

采用NaCl-KCl熔盐法成功地制备了纯钙钛矿相的铌镁酸铅基Y5V电子瓷料,系统地研究了其制备工艺、煅烧温度以及陶瓷的烧结温度、微观结构和介电性能.结果表明熔盐法制备的Y5V电子瓷料粉体不仅颗粒均匀、形貌好、易分散,而且活性高,使得多层陶瓷电容器的烧结温度可以降低到900～920℃,其介电性能要优于传统的二步合成法制备的粉体,十分有利于采用全银内浆,大大降低MLCC的生产成本.     

Glass nanocomposite of strontium bismuth niobate and lithium borate: structural and dielectric investigations

Glass nanocomposites (GNC) in the system (100−x)Li₂B₄O₇−xSrBi₂Nb₂O₉ (0≤x≤30) were prepared by splat quenching technique. The as-quenched samples of all the compositions under study have been confirmed to be amorphous by X-ray powder diffraction (XRD) studies. Differential thermal analyses (DTA) suggest the glassy nature of the as-quenched samples. High-resolution transmission electron microscopic (HRTEM) studies carried out on heat-treated samples reveal the presence of platy crystallites of SrBi₂Nb₂O₉(SBN) dispersed in the glassy matrix of Li₂B₄O₇ (LBO). The dielectric constant (ε_r) and the dielectric loss (D) decrease with increase in frequency (100 Hz–10 MHz) at 300 K. The influence of the composition and the microstructure on the dielectric properties of the LBO–SBN nanocomposite has been established. The optical transmission characteristics of these GNC could be varied as a function of its composition.     

Influence of Sr and Mn co-doping on the structural,optical, dielectric,multiferroic properties and band gap tuning in bismuth ferrite ceramics

Journal of Materials Science: Materials in Electronics - Solid state reaction was employed to synthesize the Bi1?xSrxFe1?xMnxO3 (x?=?0.05, 0.10, 0.20, 0.25) ceramic...     

Phase analysis and dielectric properties of ceramics in PbO-MgO-ZnO-Nb2O5 system: A comparative study of materials obtained by ceramic and molten salt synthesis routes

Compositions of the type 3PbO-MgO/ZnO-Nb₂O₅ were synthesized by the ceramic route at 1000°C and sintered at 1200°C. Powder X-ray diffraction studies of the 1000°C heated products show the presence of the cubic pyrochlore and the columbite (Mg/ZnNb₂O₆) type phase in the ratio of 3 : 1 for all possible combinations of MgO and ZnO. Further heating at 1200°C led to a decrease in the cubic pyrochlore phase and an increase in the columbite phase by around 10%. Compacted pellets sintered further showed the appearance of the perovskite phase. Similar compositions synthesized using the KCl-NaCl molten salt method at 900°C for 6 h gave a significant amount of the cubic perovskite related phase of the type Pb(Mg/Zn)_1/3Nb_2/3O₃ for all compositions containing MgO. The amount of the perovskite phase was nearly 55% for the Mg rich compositions and decreased with increase in Zn content, the pure Zn composition yielding mainly the cubic pyrochlore phase. On sintering these phases at 1000°C the perovskite phase content decreased. The dielectric constant of the composite materials formed by the ceramic route was in the region of 14 to 20 and varied little with frequency. The composites obtained by the molten salt method, however, showed much larger dielectric constants in the region 40–150 at 500 kHz for various compositions. The dielectric loss tangent of these composites were lower by an order (0.005–0.03 at 500 kHz) compared to the ceramic route.     

Structural,dielectric, and electrical properties of cerium-modified strontium manganite ceramics

Journal of Materials Science: Materials in Electronics - A solid-state reaction technique was used to make cerium (Ce) modified strontium manganite SrMn0.9Ce0.1O3 (SMCO). The Goldschmidt's...