The effect of glass additives on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

The effect of glass additives on the densification, phase evolution, microstructure and microwave dielectric properties of Ba(Mg_1/3Ta_2/3)O₃ (BMT) was investigated. Different weight percentages of quenched glass such as B₂O₃, SiO₂, B₂O₃-SiO₂, ZnO-B₂O₃, 5ZnO-2B₂O₃, Al₂O₃-SiO₂, Na₂O-2B₂O₃·10H₂O, BaO-B₂O₃-SiO₂, MgO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂, ZnO-B₂O₃-SiO₂ and 2MgO-Al₂O₃-5SiO₂ were added to calcined BMT precursor. The sintering temperature of the glass-added BMT samples were lowered down to 1300 °C compared to solid-state sintering where the temperature was 1650 °C. The formation of high temperature satellite phases such as Ba₅Ta₄O₁₅ and Ba₇Ta₆O₂₂ were found to be suppressed by the glass addition. Addition of glass systems such as B₂O₃, ZnO-B₂O₃, 5ZnO-2B₂O₃ and ZnO-B₂O₃-SiO₂ improved the densification and microwave dielectric properties. Other glasses were found to react with BMT to form low-Q phases which prevented densification. The microwave dielectric properties of undoped BMT with a densification of 93.1% of the theoretical density were ε_r=24.8, and Q_u×f=80,000. The BMT doped with 1.0 wt% of B₂O₃ has Q_u×f=124,700, ε_r=24.2, and . The unloaded Q factor of 0.2 wt% ZnO-B₂O₃-doped BMT was 136,500 GHz while that of 1.0 wt% of 5ZnO-2B₂O₃ added ceramic was Q_u×f=141,800 GHz. The best microwave quality factor was observed for ZnO-B₂O₃-SiO₂ (ZBS) glass-added ceramics which can act as a perfect liquid-phase medium for the sintering of BMT. The microwave dielectric properties of 0.2 wt% ZBS-added BMT dielectric was Q_u×f=152,800 GHz, ε_r=25.5, and .     

New lead-free non-stoichiometric perovskite relaxor ceramics derived from BaTiO3

The present work concerns the preparation and dielectric characterization of some new non-stoichiometric lead-free ceramics with perovskite compositions derived from BaTiO₃. Lead-free compositions could be of great interest for environment-friendly applications (dielectric for capacitors, actuators, etc.). These materials have been shown to be either classical or relaxor ferroelectrics. In the first part of this article, the BaTiO₃---Ba_0.5NbO₃ system concerns the cationic non-stoichiometry occurring only in the 12-coordination crystallographic site. In the second part, the influence of non-stoichiometry also occurring in the anionic site was determined in compositions belonging to the ternary system 2BaO---TiO₂---Nb₂O₅. The variation in the Curie temperature T_C or the temperature T_m of the maximum of ′_r decreased when the composition deviated from BaTiO₃ and when the number of vacancies increased. On the contrary, the relaxor state was favored by such a deviation.     

Characterization and physical properties of Li2O-CaF2-P2O5 glass ceramics with Cr2O3 as a nucleating agent—Physical properties

In this paper, studies on various physical properties, viz., dielectric properties (dielectric constant, loss tan δ, a.c. conductivity σ) over a wide range of frequency and temperature, optical absorption, ESR at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O-CaF₂-P₂O₅: Cr₂O₃ glass ceramics, have been reported. The optical absorption, ESR and magnetic susceptibility studies indicate that the chromium ions exist in Cr⁵⁺, Cr⁴⁺ and Cr⁶⁺ states in addition to Cr³⁺ state in these samples. The dielectric constant and loss variation with the concentration of Cr₂O₃ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analysed by a graphical method and the spreading of dielectric relaxation has been established. The a.c. conductivity in the high-temperature region seems to be connected both with electronic and ionic movements.     

A novel microwave dielectric ceramic Ca2Zn4Ti16O38: Preparation and dielectric properties

A novel microwave dielectric powder with composition of Ca₂Zn₄Ti₁₆O₃₈ was synthesized through a citrate sol-gel process. The development of crystalline phases with heat-treating temperature for the gel derived powders was evaluated by using thermo-gravimetric analysis and X-ray powder diffraction analysis techniques. The pure phase of Ca₂Zn₄Ti₁₆O₃₈ with crichtonite crystal structure was obtained at relatively low temperature of 1000 °C. The synthesized powder has high reactivity and the dense ceramics with single crystalline phase were obtained at low sintering temperature of 1100 °C. Impedance spectroscopy and microwave dielectric measurements on sintered samples showed the present compound to be a modest dielectric insulator with excellent dielectric properties of ε_r∼47-49, Qf value ∼27,800-31,600 GHz and τ_f∼+45 to +50 ppm/°C. It shows comparable microwave dielectric properties to other moderate-permittivity microwave dielectrics, but much lower sintering temperature of 1100 °C.     

Effect of the addition of B2O3 and BaO-B2O3-SiO2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu3Ti4O12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics was investigated. Both single-component (B₂O₃) and multi-component (30 wt% BaO-60 wt% B₂O₃-10 wt% SiO₂ (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B₂O₃ glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B₂O₃ content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples.     

Structural, magnetic and dielectric properties of Sc modified (1 − y)BiFeO3–yBaTiO3 ceramics

In this study, the bulk ceramics with general formula (1 − y)BiFe_1−xSc_xO₃–yBaTiO₃ (x = 0.1–0.3, y = 0.1–0.3 mol%) were prepared by the traditional solid-state method. Their structural, magnetic, dielectric properties were investigated. X-ray diffraction analysis indicated that all samples crystallized in pure perovskite structure. The structural phase transition from R3c to Pm-3m occurred when the amount of BaTiO₃ exceeded 20 mol%. The room temperature M–H curves were obtained and scandium doping could decrease the magnetic coercive field. Thus the soft magnetic property of prepared solid solutions could be improved. Frequency dependence of dielectric constant and loss were studied. The results indicated that addition of an appropriate amount of scandium could reduce the dielectric loss. The dielectric losses of 0.7BiFe_1−xSc_xO₃–0.3BaTiO₃ (x = 0, 0.1, 0.2, 0.3) at 1 kHz were 0.104, 0.094, 0.043 and 0.057 respectively.     

Some A6B5O18 cation-deficient perovskites in the BaO-La2O3-TiO2-Nb2O5 system

Some dielectric oxides have been synthesized and characterized in the BaO-La₂O₃-TiO₂-Nb₂O₅ system. Through Rietveld refinement of X-ray powder diffraction data, Ba₅LaTi₂Nb₃O₁₈ and Ba₄La₂Ti₃Nb₂O₁₈ are identified as the A_nB_n−1O_3n (n=6) type cation-deficient perovskites with space group and lattice constants , and for Ba₅LaTi₂Nb₃O₁₈; , and for Ba₄La₂Ti₃Nb₂O₁₈, respectively. Their ceramics exhibit high dielectric constant up to 57 and high quality factors (Qf) up to 21,273 GHz. The temperature coefficient of resonant frequency (τ_f) of these ceramics is decreased with the increase of B-site bond valence.     

Ferroelectric and dielectric properties of bismuth-layered structural Sr2Bi4−xLnxTi5O18 (Ln=La, Nd, Sm and Dy) ceramics

La, Nd, Sm, and Dy-doped Sr₂Bi₄Ti₅O₁₈ (SBTi) ceramic samples have been prepared by the solid-state reaction method. The X-ray diffraction reveals that all of the ceramic samples are single phase compounds. Their remnant polarization (2P_r) increases at first, and then decreases with the increase of doping content. When doping content is 0.01, Sm and Dy-doped SBTi samples exhibit the maximum 2P_r of 18.2 and 20.1 μC/cm², respectively. While La and Nd-doped SBTi samples display the maximum 2P_r value of 18.4 and 19.1 μC/cm² with doping content of 0.05 and 0.10, respectively. The ferroelectric properties of Sr₂Bi_4−xLn_xTi₅O₁₈ are found to be dominated by the competition of the decrease of oxygen vacancy concentration and the relief of structural distortion.     

花状CeO2/TiO2异质结的构筑及光催化性能

采用溶剂热法制备了三维花状CeO₂/TiO₂异质结光催化剂,然后以甲基橙(MO)为模拟有机污染物,在氙灯照射下考察了其光催化活性。结果表明,花状结构由纳米片和纳米颗粒复合而成,纳米片上均匀地附着CeO₂颗粒。Ce/Ti的物质的量之比(n_Ce/n_Ti)和溶剂热时间影响异质结的光催化性能,当n_Ce/n_Ti=0.1、溶剂热时间为6 h时,CeO₂/TiO₂的光催化活性达到最佳,氙灯照射50 min的降解率达95%,光催化活性优于纯TiO₂,这主要是CeO₂和TiO₂形成了异质结,有利于光生电子和空穴的分离。     

双层结构CeO2光阳极在染料敏化太阳能电池中的应用

利用水热法合成核壳结构Au@SiO₂@CeO₂纳米微球,制备了一系列双层结构复合光阳极并应用于染料敏化太阳能电池(DSSC)。研究表明：当CeO₂纳米微球和核壳结构Au@SiO₂@CeO₂纳米微球应用于DSSC光阳极散射层时,电池的光电转化效率有了显著提高。相对于纯TiO₂(P25)光阳极,P25/CeO₂纳米球光阳极电池的DSSC光电性能提高了15.3%,P25/Au@SiO₂@CeO₂纳米球光阳极电池的光电性能提高了27.9%。DSSC光电性能的提高主要归因于2个方面：一方面,Au纳米粒子的表面等离子体共振效应有效提高了光阳极薄膜的光散射效应。另一方面,CeO₂具有较高的染料负载能力,核壳球形结构具有较高的比表面积,增强了光的散射效应,提高了电子传输能力。     

双层结构CeO2光阳极在染料敏化太阳能电池中的应用

利用水热法合成核壳结构Au@SiO₂@CeO₂纳米微球,制备了一系列双层结构复合光阳极并应用于染料敏化太阳能电池(DSSC)。研究表明：当CeO₂纳米微球和核壳结构Au@SiO₂@CeO₂纳米微球应用于DSSC光阳极散射层时,电池的光电转化效率有了显著提高。相对于纯 TiO₂ (P25)光阳极,P25/CeO₂纳米球光阳极电池的 DSSC 光电性能提高了 15.3%,P25/Au@SiO₂@CeO₂纳米球光阳极电池的光电性能提高了27.9%。DSSC光电性能的提高主要归因于2个方面：一方面,Au纳米粒子的表面等离子体共振效应有效提高了光阳极薄膜的光散射效应。另一方面,CeO₂具有较高的染料负载能力,核壳球形结构具有较高的比表面积,增强了光的散射效应,提高了电子传输能力。     

Ag对Pd/CeO2-ZrO2-La2O3-Al2O3催化氧化甲醇性能的影响

采用等体积共浸渍法制备了一系列Pd-Ag/CeO2-ZrO2-La2O3-Al2O3催化剂。运用N2吸附-脱附,X射线衍射(XRD),H2程序升温还原(H2-TPR),紫外-可见漫反射光谱(UV-Vis DRS),X射线光电子能谱(XPS)对催化剂进行表征,并考察其对甲醇的催化氧化性能。活性测试结果表明,Ag的添加可显著改善Pd催化剂对甲醇的催化氧化活性,T50、T90以及ΔT分别为125℃,150℃和25℃,具有较好的应用前景。H2-TPR表明,引入Ag可明显改善催化剂的还原性能,使表面易还原氧物种量增多,还原速率加快;UV-Vis DRS及XPS表明,Pd、Ag金属之间以及金属与载体之间存在电子效应,这种效应促使金属与载体界面产生大量具有活性的氧物种,不仅提高了催化剂的低温活性,还提高了催化剂的氧化速率。     

Preferential oxidation of CO in excess H2 over CeO2/CuO catalyst:Effect of calcination temperature

Different from the classical configuration CuO/CeO2 catalyst,the inverse configuration CeO2 /CuO catalyst (atomic ratio of Ce/Cu=10/100) was prepared by impregnation method.Five calcination temperatures were selected to investigate the interaction between CeO2 and CuO support.It is found that as calcination temperature increased from 500 to 900 C,sintering of CeO2 particles on the support occurred together with the diffusion of a portion of Ce 4+ ions into CuO crystals,forming solid solution.Formation of interface complex Ce-O-Cu was suggested by TPR measurements.The catalyst calcined at 700 C gives the highest activity for preferential oxidation of CO in excess H2 stream.     

片状纳米结构CeO2晶体的制备及其吸附CO2性能

在室温下,将CeCl₃溶液与CO₂储存材料（CO₂SM）混合、搅拌0.5 h制备了片状碳酸铈前驱体（CCPs）,并在500℃下煅烧CCPs 4 h,制得平均尺寸为4.94 μm×0.92 μm,厚度为0.04~0.08 μm纳米结构片状CeO₂晶体。在此过程中,CO₂SM不但可以提供CO₃^2-,还能起到分散剂和结构导向剂的作用。反应过程中,系统地研究了CO₂SM用量、Ce³⁺浓度和搅拌时间3个因素对CCPs形态和大小的影响,得到最优制备条件：0.1 g CO₂SM和50 mL 0.03 mol·L^-1 Ce³⁺水溶液以1 000 r·min^-1转速在室温下搅拌0.5 h。煅烧CCPs后,所制备的片状CeO₂晶体在室温下CO₂吸附量可达0.554 mmol·g^-1。     

CeO2-MnOx催化剂上氯乙烯有机废气的催化燃烧

采用柠檬酸(CA)溶胶-凝胶法制备了不同Mn:(Ce+Mn)摩尔比的CeO2-MnOx催化剂,以氯乙烯有机废气的催化燃烧为模型反应,考察了催化剂制备条件和反应条件对于CeO2-MnOx催化剂性能的影响,并用N2吸附、X射线衍射(XRD)和H2程序升温还原(H2-TPR)对催化剂进行了表征.结果表明,CeO2-MnOx催化剂上氯乙烯燃烧反应产物只有HCl,H2O和CO2,没有检测到其他氯代烃和氯气等副产物.当CA:Mn:Ce=0.3:0.50:0.50时,所制备的CeO2-MnOx催化剂活性最高,对于较宽的空速范围(10000～30000h-1)和较宽的浓度范围(0.05%～0.15%),低浓度氯乙烯的催化燃烧反应具有较好的操作弹性.其中当氯乙烯浓度为0.1%,空速为15000h-1时,起燃温度T50=110oC,完全转化温度T99=220oC.XRD和H2-TPR结果表明,在CeO2-MnOx催化剂中只出现立方相萤石结构CeO2的特征衍射峰,没有出现MnOx物种的特征衍射峰;Mn离子进入CeO2晶格形成的Ce-Mn-O固溶体,有利于提高催化剂表面的活性氧物种的活性,乃至催化剂活性.     

微波场对SrTiO3化学合成中热过程的影响

在分析微波场中SrTiO3化学合成体系与电磁场相互作用的基础上,探讨合成体系在微波场中的加热机制和影响升温的主要因素（如合成体系的介电性质、保温材料的结构、生还的致密度等）,结果表明,TiO2和SrCO3在低温阶段对体系的升温速率的贡献相接近;高温阶段体系升温主要是TiO2的贡献,同时产物对升温有较大的影响。微波合成与常规合成再加热方式上的明显不同,对合成过程、合成时间等影响较大。     

Preparation and Dielectric Properties of Mn-Doped Ba0.6Sr0.4TiO3-MgTiO3 Composite Ceramics

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) nano-powders were prepared using Ba(NO₃)₂, Sr(NO₃)₂, oxalic acid dehydrate, and tetrabutyl titanate (Ti(OC4H9)4) as precursors by the chemical co-precipitation method. The product was characterized by thermogravimetry-differential scanning calorimetry (TG-DSC) thermal analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results indicated that the resulting Ba_0.6Sr_0.4TiO₃ nano-powders were homogeneous with agglomerated nature. The Ba_0.6Sr_0.4TiO₃-MgTiO₃ (BST-MT) bulk composite ceramics doped by Mn were obtained by the traditional solid phase method. The XRD patterns demonstrated that Mn-doped BST was unable to change the perovskite crystalline structure of BST materials. SEM photographs revealed that the crystalline grains became larger with increasing the content of doping Mn (<1.5% (x, molar fraction)) and then the size of grains decreased after the Mn content exceeded 1.5% in the BST ceramics, suggesting the effect of Mn doping on the morphologies of BST-MT composites. The dielectric properties of BST-MT composite ceramics doped with 0.1%-2.0% (x) Mn were investigated systematically. Two effects of Mn doping on the dielectric properties of the BST-MT composite ceramics were observed. At low Mn doping concentrations (<1.5%), Mn mainly acted as an acceptor dopant to replace Ti at the B site of ABO3 perovskite structure, leading to a diffused phase transition. It was also observed that the grain size increased drastically as the Mn content increased and thus caused the decrease of dielectric loss. At higher Mn doping concentrations (>1.5%), the grain size decreased and the suppression of permittivity and the drastic increase of the dielectric losses were observed, which indicated a “composite” mixing effect.     

CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了Ca O或Ba O与Sm2O3共掺杂Ce O2体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时Ba Sm Ce30O63体系最稳定;Sm靠近,Ca远离氧空位时Ca Sm Ce30O63体系最稳定。Ba Sm Ce30O63和Ca Sm Ce30O63体系中均不存在Ce4+变价。对Ca Sm Ce30O63体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为Em(3→V)Em(1→V)Em(4→V)Em(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对Ba Sm Ce30O63体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为Em(V→3)Em(V→5)Em(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,Ca Sm Ce30O63体系最小迁移能小于Sm Ce31O63体系,证实了Ce O2-Sm2O3-Ca O体系离子电导率大于Ce O2-Sm2O3体系的实验结果。     

Effect of magnetostrictive phase on structural, dielectric and electrical properties of NiFe2O4 + Pb0.93La0.07(Zr0.60Ti0.40)O3 composites

Particulate composites of NiFe₂O₄ (NFO) and Pb_0.93La_0.07 (Zr_0.60Ti_0.40) O₃ (PLZT) were synthesized by solid-state reaction technique. Structure and surface morphological studies were carried out using X-ray diffraction and scanning electron microscopy techniques, respectively. Frequency dependent variation of dielectric constant (), loss tangent (tan δ) and ac resistivity for (x) NFO + (1−x) PLZT composites in the range 100 Hz–5 MHz at room temperature were studied. The temperature dependence of dielectric constant (′), loss tangent (tan δ) was studied in wide temperature range of measurement at fixed frequencies. Also DC resistivity measurements were carried out in the temperature range of 300 K–923 K. Structural, dielectric and electrical properties show notable change due to presence of magnetostrictive NFO phase along with PLZT.     

Synthesis and characterization of sodium titanates Na2Ti3O7 and Na2Ti6O13

Na₂Ti₃O₇ and Na₂Ti₆O₁₃ were synthesized by sol-gel method in order to obtain pure phases. Different heat-treatments were applied on powders and pellets of these materials. The effects were studied by XRD, dilatometry, TGA-DTA, SEM and electrochemical impedance spectroscopy. Pure Na₂Ti₃O₇ was obtained at 973 K. Sintering at 1373 K caused a partial decomposition into Na₂Ti₆O₁₃. The Na₂Ti₃O₇ powder sintered at 1273 K showed polygonal microstructure. Na₂Ti₃O₇ pellets sintered at 1323 K for 10 h exhibited large structures. This latter microstructure decreased the electrical conductivity of Na₂Ti₃O₇. Pure Na₂Ti₆O₁₃ was obtained at 873 K. Sintering at 1073 K caused a partial decomposition into TiO₂ (rutile). Na₂Ti₆O₁₃ pellets sintered at 1323 K for 10 h exhibited common shrinkage behavior. This shrinkage process increased the electrical conductivity of this material. The presence of TiO₂ resulted in a oxygen partial pressure dependence of the electrical conductivity.