Effects of Li2CO3 on the sintering behavior and piezoelectric properties of Bi2O3-excess (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics doped with Li₂CO₃ and Bi₂O₃ as sintering aids were manufactured, and their micro structural, dielectric and piezoelectric properties were investigated. All specimens could be well sintered at a low-temperature of 1080 °C. The bulk density of the specimens doped with a small amount of Li₂CO₃ was enhanced. The dielectric and piezoelectric properties of ceramics were investigated with different amounts of Li₂CO₃ substitutions. High electrical properties of d₃₃ = 167 pC/N, k_p = 0.34, P_r = 40 μC/cm² and E_c = 38 kV/cm were obtained from the specimen containing 0.1 mol% of Li₂CO₃ sintered at 1080 °C.     

Effect of BiFeO3 addition on Bi2O3–ZnO–Nb2O5 based ceramics

In this paper, low temperature sintering of the Bi₂(Zn_1/3Nb_2/3)₂O₇ (β-BZN) dielectric ceramics was studied with the use of BiFeO₃ as a sintering aid. The effects of BiFeO₃ contents and the sintering temperature on the phase structure, density and dielectric properties were investigated. The results showed that the sintering temperature could be decreased and the dielectric properties could be retained by the addition of BiFeO₃. The structure of BiFeO₃ doped β-BZN was still the monoclinic pyrochlore phase. The sintering temperature of BiFeO₃ doped β-BZN ceramics was reduced from 1000 °C to 920 °C. In the case of 0.15 wt.% BiFeO₃ addition, the β-BZN ceramics sintered at 920 °C exhibited good dielectric properties, which were listed as follows: ε_r = 79 and tan δ = 0.00086 at a frequency of 1 MHz. The obtained properties make this composition to be a good candidate for the LTCC application.     

Ferroelectric phase transition and optical performance of PLZnNZT transparent ceramics

Lead-based Pb_0.97La_0.02(Zn_1/3Nb_2/3)_0.3(Zr_0.53Ti_0.47)_0.7O₃ (PLZnNZT) transparent ceramics with the addition of 2 wt% excess PbO were prepared by hot-pressing sintering method. The hot-pressing sintered PLZnNZT ceramics exhibit dense and large-grained microstructure, and perovskite structure with distorted cubic-like symmetry. The ceramics exhibit normal ferroelectric-like dielectric behavior with slightly diffused ferroelectric phase transition characteristic. The PLZnNZT ceramics exhibit fully developed, symmetric and saturated P–E hysteresis loop and large piezoelectric constant d₃₃, being 468 pC/N. The ceramics with 120 μm thickness exhibit maximum transmittance of 53% at 850 nm when Fresnel losses was not included, almost totally transparent in the mid IR region (2500–5600 nm), and low-lying optical band gap energy E_g of 3.23 eV. Three diffused Raman bands centering around 240 cm⁻¹, 560 cm⁻¹ and 750 cm⁻¹ are observed by micro-Raman spectroscopy, which can be attributed to F2g [BO₆] bending vibration, A1g [BO₆] stretching vibration and “soft mode” mixed by the bending and stretching vibrations, respectively, confirming the normal ferroelectric-like characteristic.     

The effects of sintering temperatures on dielectric,ferroelectric and electric field-induced strain of lead-free Bi0.5(Na0.78K0.22)0.5TiO3 piezoelectric ceramics synthesized by the sol–gel technique

Lead-free Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (BNKT) piezoelectric ceramics were synthesized by the sol–gel technique. The effects of sintering temperatures on the crystal structure, microstructure, densification, dielectric, ferroelectric and electric field-induced strain behaviors of the BNKT ceramics were investigated. X-ray diffraction patterns exhibited a pure perovskite structure from 1075 to 1150 °C. A scanning electron microscopy study revealed an increase in grain size with increasing sintering temperature. The density of the ceramics sintered at 1150 °C reaches a maximum value of 5.55 g/cm³, which is 96% of the theoretical density. BNKT ceramics sintered at an optimum temperature of 1150 °C exhibited a high remnant polarization of 18.5 μC/cm², a high electric field-induced strain of 0.20% and dynamic piezoelectric coefficient d₃₃¹ = (S_max/E_max) of 247 pm/V.     

Improved properties & fatigue resistant behaviour OF Ba(Zr0.15Ti0.85)O3 ferroelectric ceramics

The microstructure, dielectric and piezoelectric properties of Zr doped BaTiO₃ ceramics sintered at optimum temperature, are investigated. High energy ball milling technique is adopted to realize nano-sized powders of Ba(Zr_0.15Ti_0.85)O₃ ceramics. Increased boundary mobility of fine powders aided to obtain a relative density of >98.8% of theoretical density corresponding to ceramics under study. Internal stresses in these ceramics are found to be relieved by grain-boundary sliding. The Ba(Zr_0.15Ti_0.85)O₃ ceramics synthesized at relatively low sintering temperatures exhibit remarkable, enhanced dielectric properties viz. improved polarization, high unipolar strain values comparable to Zr doped BaTiO₃ single crystals of same composition, at relatively lower electric fields and also exhibit better fatigue tolerant properties. The underlying mechanisms responsible for superior dielectric, ferroelectric and piezoelectric properties are discussed.     

Peculiarities of luminescent properties of cerium doped YAG transparent nanoceramics

Optical and luminescence properties of transparent nanosized cerium doped Y₃Al₅O₁₂ (YAG:Ce) ceramics have been studied. YAG:Ce nanoceramics were obtained by means of low temperature and high pressure (LTHP) sintering method. Nanoceramic samples were sintered in the 2–8 GPa pressure range, whereas Ce³⁺ concentration was varied in the 0.5–5 at. % range. It is shown that, in contrast to the single crystal, a strong rise of absorption coefficient was detected already at wavelength shorter than 400 nm in all nanoceramic samples studied. Furthermore, in nanoceramic samples unusual UV emission band near 3.1 eV was observed, which is not observed in the YAG:Ce single crystal. High pressure applied during nanoceramics sintering leads to significant changes in their optical and luminescence properties.     

铌酸钾钠基无铅透明陶瓷制备及性能

采用传统固相烧结工艺, 结合特殊的气氛控制技术,制备了铌酸钾钠(KNN)基无铅透明陶瓷 xBa(Sc_0.5Nb_0.5)O₃-(1-x) (K_0.5N_0.5)NbO₃ (简写xBSN-(1-x)KNN). 并对其微观结构、介电、铁电性能和光学透光率进行了研究. 结果表明该体系陶瓷具有准立方钙钛矿结构, 没有其他杂相, 晶粒大小与可见光波长相当, 高度致密, 无明显的晶界存在. 在 x=0.05时, d₃₃最高可达到110 pC/N, 2P_r达到25.4 μC/cm². 同时该材料具有良好的透明性, 在可见光范围内,透过率达到54%左右, 近红外2500 nm处,透过率接近83%, 是一种有望取代铅基透明陶瓷的环境友好型无铅透明陶瓷.     

Effect of sintering temperature on structure and nonlinear dielectric properties of Ba0.6Sr0.4TiO3 ceramics prepared by the citrate method

Ba_0.6Sr_0.4TiO₃ ceramics were prepared by a citrate precursor method. The structure and nonlinear dielectric properties of the resulting ceramics were investigated within the sintering temperature range 1200-1300 °C. Adopting fine Ba_0.6Sr_0.4TiO₃ powder derived from the citrate method was confirmed to be effective in reducing the sintering temperatures required for densification. The ceramic specimens sintered at 1230-1280 °C presented relative densities of around 95%. A significant influence of sintering temperature on the microstructure and nonlinear dielectric properties was detected. The discrepancy in nonlinear dielectric behavior among the specimens sintered at different temperatures was qualitatively interpreted in terms of the dielectric response of polar micro-regions under bias electric field. The specimens sintered at 1230 and 1250 °C attained superior nonlinear dielectric properties, showing relatively low dielectric losses (tan δ) of 0.24% and 0.22% at 10 kHz together with comparatively large figure of merits (FOM) of 121 and 142 at 10 kHz and 20 kV/cm, respectively.     

Microstructures and microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1-xB_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm³, a dielectric constant (ε_r) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τ_f) of −86 ppm/°C were obtained for La_0.995B_0.005(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h.     

Preparation and characterization of CaTiO 3 –(Li 1/2 Nd 1/4 Sm 1/4 )TiO 3 microwave ceramics by a sol–gel combustion process

A novel sol–gel combustion process was adopted to synthesize reactive ceramic powder with composition of 0.25 CaTiO₃–0.75 (Li_1/2Nd_1/4Sm_1/4)TiO₃, and microwave dielectric ceramics were prepared at different sintering temperatures using the synthesized powder. The combustion behavior of citrate gel and the sintering feature of the synthesized powder were evaluated by using differential thermal analysis–thermogravimetric analysis and thermo-mechanical analysis techniques, respectively. The citrate gel exhibits a self-propagating behavior after being ignited in air at room temperature. The as-burnt powder is so highly reactive that it can be transformed into single-phase perovskite at 900 °C and it can be sintered at 1100 °C. The effects of sintering temperature on the density, microstructure, and dielectric properties of the sintered ceramics were investigated. The maximum values of density, dielectric constant, and Q×f were achieved after sintering at 1200 °C. At 1200 °C, very dense ceramics with uniform grains and good dielectric properties with a dielectric constant of 123.8, a Q×f value of 5110 (at 3.7 GHz), and a τ_f value of +12.5 ppm/°C were achieved via the sol–gel combustion route. PACS 77.84.Dy; 81.20.FW; 77.22.-d     

Yb:Y2－2xLa2xO3激光透明陶瓷的光谱性能

对一种低温易烧结的Yb:Y_2-2xLa_2xO₃激光透明陶瓷的光谱性能进行了初步研究，Yb:Y_2-2xLa_2xO₃激光透明陶瓷具有宽的吸收带和大的吸收截面，在最强的吸收峰977nm处吸收截面达4.0×10^-20cm²；其荧光发射寿命为1.1ms，发射截面在1033nm处为1.0×10^-20cm²，在1077nm处为0.7×10^-20cm².Yb:Y_2-2xLa_2xO₃陶瓷的各项光学性能指标接近或达到单晶的指标. 关键词： 氧化镧钇 激光陶瓷 低温烧结 光谱性能     

Spectroscopic characterization of Yb:Sc2O3 transparent ceramics

Yb：Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm-1. There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth （11 nm） and an emission cross-section of 1.8×10^-20 cm^2. The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb：Sc2O3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb：Sc2O3 transparent ceramics are a promising material for short pulse lasers.     

Synthesis of SmAlO<Subscript>3</Subscript> nanocrystalline powders by polymeric precursor method

SmAlO₃ nanocrystalline powders were successfully synthesized by the polymeric precursor method using ethylenediaminetetraacetic acid as a chelating agent. The precursor and the derived powders were characterized by thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), infrared spectroscopy (IR), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The results showed that pure SmAlO₃ powder with orthorhombic perovskite structure could be synthesized at 800°C for 2 h without formation of any intermediate phase. The average particle size of the powder synthesized at 900°C was as low as 28 nm. Subsequently, the bulk SmAlO₃ ceramics were prepared at various sintering temperatures using the synthesized powders calcined at 900°C for 2 h as starting materials. The sintering experiments indicated that the sample sintered at 1550°C for 2 h exhibited the highest relative density of 97.2% and possessed the best microwave dielectric properties of ε _r=20.94, Q×f=78600 GHz and τ _f=−71.8 ppm/°C.     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting La3+ with Sm3+

The microwave dielectric properties of La_1?xSm_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1?xSm_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.59 g/cm³, dielectric constant (ε_r) of 19.9, quality factor (Q×f) of 70,200 GHz, and temperature coefficient of resonant frequency (τ_f) of ?77 ppm/°C were obtained for La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h. The dielectric constant, and τ_f of La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics were almost independent with the sintering temperature as the sintering temperature varied from 1450 to 1600 °C.     

Effect of Cu-stoichiometry on the dielectric and electric properties in CaCu3Ti4O12 ceramics

CaCu_3+yTi₄O₁₂ (y=0, ±0.025, ±0.05, ±0.1 and −0.15) ceramics are prepared by the conventional solid-state reaction technique under sintering condition of 1050 ^°C, 10 h. X-ray diffraction shows that they all have the good crystalline structure. Cu-deficient ceramics exhibit the microstructures of uniform grain size distribution, whereas both Cu-stoichiometric and Cu-rich ceramics display microstructures of bimodal grain size distribution. The largeness of low-frequency dielectric permittivity at room temperature is found to be very sensitive to the Cu-stoichiometry. Upon raising the measuring temperature, all of the ceramics present commonly three semicircles in the complex impedance plane. It indicates that there exist three distinct contributions, which are ascribed to arising from domains, grain boundaries and domain boundaries. In addition, the influence of CuO segregation on the dielectric and electrical properties is also discussed.     

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y₂O₃:R(R = Yb³⁺, Er³⁺, Tm³⁺) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er³⁺/5 mol% Yb³⁺/xTm³⁺ tri-doped Y₂O₃ nanophosphors were sintered at 1000 ^°C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm³⁺ concentration from 0 to 0.5 mol%, because the Tm³⁺ state can be easily reached due to the ²F_7/2 → ²F_5/2 transition of Yb³⁺ near 10,000 cm⁻¹. The Y₂O₃: Er³⁺/Yb³⁺/Tm³⁺ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.     

Synthesis,structural and electrical properties of double perovskite Sr<Subscript>2</Subscript>NiMoO<Subscript>6</Subscript> ceramics

The double perovskite Sr₂NiMoO₆ powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained when calcined in air at 1300°C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric properties (ε _r and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280°C for conventional route, while no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different starting processes affected the phase formation behavior and the electrical properties of Sr₂NiMoO₆ ceramics.     

Microstructure and dielectric properties of Li2CO3 doped 0.7(Ba,Sr)TiO3–0.3MgO ceramics

Microstructure and dielectric properties of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃–0.3MgO ceramics for the low temperature sintering and microwave applications will be presented. In these days, low temperature sintering process has been widely spread out for the integrated electronic modules for the communication systems such as front-end modules, antenna modules, and switching modules. We have added Li₂CO₃ and MgO to (Ba,Sr)TiO₃ material to reduce the sintering temperature and improve dielectric properties such as loss tangent, and frequency dispersion.In this paper, we have discussed the crystalline properties, dielectric properties, and the microstructures of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃–0.3MgO ceramics. No pyro phase was observed in the X-ray diffraction method. Very weak frequency dispersion (<0.7%) of dielectric permittivity was observed from the 1 kHz to 1 MHz range. We found that the grain size of BST is around 2 μm, while the grain size of Li₂CO₃ dope 0.7BST–0.3MgO is around 4 μm from the SEM analysis.     

Enhanced dielectric and nonohmic properties of SrTiO3-modified CaCu3Ti4O12 ceramics

Dielectric and nonohmic properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics can be modified by addition of SrTiO₃ (STO) in different molar proportions which were fabricated by a modified sol-gel method. XRD results indicated that all modified ceramics showed mixed phase consisting of both CCTO and STO. SEM images and grain size distribution probability also presented the change of microstructure with the addition of STO. The dielectric loss of the CCTO/0.4STO ceramics sintered at 1000 °C can be lower than 0.02 in a wide frequency (1 kHz–10 kHz), especially at 1 kHz, the dielectric loss of this sample is as low as 0.012. Furthermore, excellent nonlinear I–V electrical characteristic (high breakdown voltage to 54.15 kV/cm for CCTO/0.4STO sintered at 1000 °C) was observed as well. All the results indicated that the addition of STO does improve the dielectric properties and nonohmic characteristics of CCTO ceramics dramatically.     

Enhanced piezoelectric properties near the morphotropic phase boundary in lead-free (1-x)(Bi0.5K0.5)TiO3-xBi(Ni0.5Ti0.5)O3 ceramics

Lead-free piezoelectric ceramics of the composition (1-x)(Bi_0.5K_0.50)TiO₃-xBi(Ni_0.50Ti_0.50)O₃ or (1-x)BKT-xBNiT (when x = 0–0.20 mol fraction) were prepared by a conventional mixed-oxide method and sintered at 1050 °C for 4 h. The effects of BNiT content on the phase equilibria, and the dielectric, ferroelectric and piezoelectric properties were systematically investigated. High density sintered specimens (5.71–6.12 g/cm³) were obtained for all compositions. X-ray diffraction patterns showed that all BKT-BNiT samples exhibited a single perovskite phase which confirms that BNiT and BKT formed a solid solution up to x = 0.20. A morphotropic phase boundary (MPB) separating a BKT-rich tetragonal phase and a BNiT pseudo-cubic phase was identified over the compositional range 0.05 < x < 0.10, where enhanced electrical properties were observed. The optimum dielectric properties (ε_r = 1710, tanδ = 0.036), ferroelectric properties (P_r = 16.6 μC/cm², E_c = 22.5 kV/cm and R_sq = 0.86) and piezoelectric properties (d₃₃ = 288 pC/N, S_max = 0.22% and d^*₃₃ = 313 pm/V) were observed with a relatively high T_m ∼ 304 °C within this MPB region. Overall, these results indicate that the BKT-BNiT ceramic system is a promising lead-free piezoelectric candidate for further development for actuator applications.