Low temperature sintering and microwave dielectric properties of Ba4Sm9.33Ti18O54 ceramics

The effect of BaCu(B₂O₅) (BCB) on the sinterability, microstructure and microwave dielectric properties of Ba₄Sm_9.33Ti₁₈O₅₄ (BST) has been investigated. Dilatometric measurements reveal that the sintering temperature of BST can be reduced by the addition of BCB. Microstructural analysis shows abnormal grain growth with large amount of BCB. A ceramic composite with Q × f = 4000 GHz, ?_r = 52 and τ_f = ?29 ppm/°C which can be sintered at 950 °C is obtained when 10 wt% BCB is added to BST. EDS analysis shows that the composite is chemically compatible with silver.     

Modification of Ba4Sm2Ti4Ta6O30 dielectric ceramics

Modification of promising tungsten bronze-type dielectric ceramic Ba₄Sm₂Ti₄Ta₆O₃₀ has been investigated by adjusting the composition in Ba_4-3xSm_2+2xTi₄Ta₆O₃₀. The temperature coefficient of dielectric constant has been significantly improved by such modification together with the suppressed dielectric loss, but the dielectric constant decreased significantly. © 2000 Kluwer Academic Publishers     

溶胶-凝胶法制备Ba_(3.99)Sm_(9.34)Ti_(18)O_(54)微波介质陶瓷粉体

用柠檬酸(C6H8O7)为络合剂,以硝酸钐(Sm(NO3)3)、钛酸四丁酯(C16H36O4Ti)、硝酸钡(Ba(NO3)2)为原料,采用溶胶-凝胶法制备单相Ba3.99Sm9.34Ti18O54微波介质陶瓷粉体。采用差热分析、X射线衍射表征Ba3.99Sm9.34Ti18O54前驱体的热行为和晶型转化过程,用场发射扫描电镜对粉体的形貌进行表征。结果表明:在1000℃下保温3h可以获得纯Ba3.99Sm9.34Ti18O54陶瓷粉体,形状为不规则片状,平均粒径为100~200nm。     

PbTiO3+Bi2Ti2O7掺杂的Ba4.5Nd9Ti18O54微波介质陶瓷

研究了PbTiO3 Bi2Ti2O7掺杂的Ba4.5Nd9Ti18O54微波介质陶瓷材料的结构和介电性能.结果表明,随着掺杂量的增加,陶瓷材料的密度呈现出轻微下降的趋势,介电常数则保持较高的数值,Q值及τf随掺杂量的增加而下降.当PbTiO3 Bi2Ti2O7掺杂量为20%时,材料的εr≈93,Q.f≈5800 GHz,τf≈3×10-5/℃.XRD分析表明,当PbTiO3 Bi2Ti2O7掺杂量小于24%时,Ba4.5Nd9Ti18O54材料仍呈现出单相结构.利用电介质极化理论初步解释了材料介电性能变化的原因.     

Low temperature sintering and dielectric properties of Ba2Ti3Nb4O18 ceramics for silver co-sintering application

Low temperature sintering and dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with ZnO–B₂O₃–SiO₂ (ZBS) frit and lithium salts addition were investigated for silver co-sintering application. The sintering temperature of dense Ba₂Ti₃Nb₄O₁₈ ceramics with ZBS frit or LiNO₃ addition was effectively lowered to 950 or 1,000 °C, respectively. LiNO₃ is found to be more efficient than LiF or Li₂CO₃ to lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramics. The sintering temperature of 900 °C was obtained for the Ba₂Ti₃Nb₄O₁₈ ceramics with a combination of ZBS frit and LiNO₃ addition. The dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with 1 wt.% ZBS and 0.5 wt.% LiNO₃ sintered at 900 °C are as follows: ε_r ~ 37.8, tan δ ~ 0.0003, τ_ε ~ 4.6 ppm/°C.     

Characterization of Ba4.5Re9Ti18O54 (Re = La,Nd) microwave dielectric ceramics

Ba_4.5Re₉Ti₁₈O₅₄ (Re = La, Nd) ceramics were prepared via a solid state mixed oxide route. X-ray diffraction (XRD) analysis revealed the formation of the major Ba_4.5Re₉Ti₁₈O₅₄ phase along with rutile (TiO₂) as a secondary phase. Rietveld structure refinement of the recorded XRD data confirmed that the crystal structure of Ba_4.5Nd₉Ti₁₈O₅₄ (BNT) was orthorhombic (Pnma) with unit cell parameters a = 22.3412 Å, b = 7.6824 Å and c = 12.1952 Å. Ba_4.5La₉Ti₁₈O₅₄ (BLT) exhibited high relative permittivity (95.6), low quality factor (2,102 GHz) and a high temperature coefficient of resonance frequency (+352 ppm/°C). The substitution of Nd for La caused a decrease in both the relatively permittivity and temperature coefficient of resonance frequency to 84.2 and 167 ppm/°C respectively and an increase in quality factor to 8,007 GHz. Raman spectroscopic analysis revealed that lattice defects may be responsible for the observed decrease in quality factor of BLT ceramics in comparison to BNT. The Raman shifts at 533.5 and 613.6 cm^?1, related to Ti–O bond stretching, decreased for BNT ceramics, which may be a possible reason for the observed decrease in relative permittivity.     

Ba3.75Nd9.5Ti18O54的液相法合成

以柠檬酸为络合剂,乙二醇为酯化剂,利用液相混合法合成了Ba3.75Nd9.5Ti18O54陶瓷粉末.研究了不同的CA/M值(柠檬酸与金属离子总浓度的摩尔比)对粉末的结晶特性的影响,利用DTA,TGA和XRD等技术分析了前驱体和得到的氧化物的特性.当CA/M=2时,将前驱体在900℃预烧3h可直接得到结晶良好的Ba3.75Nd9.5Ti18O54粉末.     

Ba4(Nd0.85Bi0.15)28/3Ti18O54陶瓷低温化研究

采用复合添加BaCuO2-CuO和BaO-B2O3-SiO2助剂的方法,研究了Ba4(Nd0.85Bi0.15)28/3 Ti18O54陶瓷的低温烧结特性和微波介电性能.添加2.5wt?CuO2-CuO和5wt?O-B2O3-SiO2后Ba4(Nd0.85 Bi0.15)28/3 Ti18O54陶瓷在950℃烧结成瓷,气孔率为5.29%,介电常数ε为60.25,Q·f值为2577GHz(5.6GHz),频率温度系数τf为 25.1ppm/℃,可与Cu电极浆料低温共烧.     

Ba4Nd2Ti4Ta6O30 dielectric ceramics modified by Bi substitution for Nd

Modification of dielectric properties for Ba₄Nd₂Ti₄Ta₆O₃₀ ceramic was investigated through Bi partial substitution for Nd. The dielectric constant increased and the dielectric loss decreased with increasing concentration of Bi, and the dielectric constant reached 142, combined with a low dielectric loss of 10^–4 (at 1 MHz) for the composition Ba₄(Nd_0.975Bi_0.025)₂Ti₄Ta₆O₃₀. The temperature coefficient () can be slightly improved.     

Effect of TiO2 and Al2O3 doping on sintering behavior and microwave dielectric properties of Ba4(Sm0.5Nd0.5)28/3Ti18+xO54+2x ceramics

The effects of TiO₂ and Al₂O₃ doping on the phase formation, the microstructure and microwave dielectric properties of Ba_6?3x (Sm_1?y ,Nd _y )_8+2x Ti₁₈O₅₄ (x = 2/3 and y = 0.5; BSNT) ceramics were investigated. X-ray diffraction patterns showed that the main crystal phase of BSNT + xTiO₂ (x = 0–2) ceramics sintered at 1,280 and 1,300 °C for 5 h was Ba(Sm, Nd)₂Ti₄O₁₂, accompanied by a small number of second phases: Ba₂Ti₉O₂₀ and TiO₂ (x ≥ 1.0), while the new phase BaAl₂Ti₅O₁₄ appeared and the two phases Ba₂Ti₉O₂₀ and TiO₂ disappeared in BSNT ? 2TiO₂ ceramic doped with ≥2 wt% Al₂O₃ successively as identified by scanning electron microscopy and energy dispersive spectroscopy analysis. The TiO₂ and Al₂O₃ working as sintering aids conduced effectively to promote the densification and grain growth, and thus decreasing the sintering temperature, so when the amounts of TiO₂ was increased, Q × f and τ _f values increased continuously. The BSNT ? 2TiO₂ ceramics doped with y wt% Al₂O₃ decreased the density and dielectric constant, increased the Q × f value remarkably and the τ _f values was adjusted from 25.3 to ?7.3 ppm/ °C. When doped with 1.5 wt% Al₂O₃ sintered at 1,260 °C for 5 h, the ceramics obtained the excellent microwave dielectric properties: ε _r  = 74.3, Q × f = 11,928 GHz, and τ _f  = +5.39 ppm/ °C.     

Synthesis and microwave dielectric properties of Ba4Ti3P2O15 ceramics

Present work introduces a new kind of microwave dielectric ceramic, Ba₄Ti₃P₂O₁₅. Ba₄Ti₃P₂O₁₅ ceramic can be prepared by solid state reaction method and be well densified after being sintered at above 1175 °C for 4 h in air. All the XRD patterns can be fully indexed as single-phase structure. The best microwave dielectric properties can be obtained in ceramic sintered at 1200 °C for 4 h with permittivity about 20.7, Q × f about 42,210 GHz and TCF about 37 ppm °C^?1. Measurements of the microwave dielectric properties of Ba₄Ti₃P₂O₁₅ ceramic revealed the existence of a maximum in the temperature dependence of the dielectric loss because of the defect dipoles relaxation.     

Preparation and characterization of NiMn2O4 negative temperature coefficient ceramics by solid-state coordination reaction

The influence of synthesis parameters, such as calcination temperature and sintering temperature, on the microstructure, phase composition, and electrical properties of NiMn₂O₄ negative temperature coefficient (NTC) ceramics was systematically investigated. The NiMn₂O₄ NTC ceramics were synthesized via solid-state coordination reaction. With increasing sintering temperatures, the relative density increased, whereas the porosity decreased. Single-phase, cubic spinel ceramic was obtained following sintering at 900 and 1,050 °C, whereas a secondary phase, i.e., NiO, was detected when the sintering temperature was higher than 1,100 °C. High-density ceramics were obtained when the sintering temperature was higher than 1,100 °C, and featured the lowest room temperature resistivity of 2,924 Ω cm and thermal constant B of 3,429 K. The latter parameter reflects the temperature sensitivity of the NTC ceramics. Variations of the electrical property were because of increases in density and onset of decomposition.     

模板晶粒生长技术制备SrBi2Nb2O9织构陶瓷

以熔盐法制备的片状SrBi2Nb2O9晶体为模板剂,采用模板晶粒生长技术和流延法制备了Sr-Bi2Nb2O9织构陶瓷,研究了模板含量对SrBi2Nb2O9织构陶瓷烧结行为、织构度、显微结构的影响。结果表明:模板含量为10wt%时,1200℃保温2h烧结可获得体积密度最大的SrBi2Nb2O9织构陶瓷,模板含量继续增加,体积密度降低;织构陶瓷的晶粒尺寸随模板含量的增加而逐渐增大,且晶粒取向性生长趋于明显,当模板含量为10wt%时,织构化SrBi2Nb2O9陶瓷的晶粒取向率f达到最大值,为0.81;织构化陶瓷的压电常数d33达到13pC/N,高于固相法制备的陶瓷的压电常数。     

Mn掺杂改性高温无铅压电陶瓷CaBi4Ti4O15的研究

用固相合成法制备Mn掺杂改性的CaBi4Ti4O15（CBT）高温无铅压电陶瓷。分析表明，利用固相合成法制备Mn掺杂CBT的温度为850℃，制备Mn掺杂改性CBT陶瓷的烧结温度随锰含量的增加降低，压电常数影响不大。     

Microstructure and dielectric relaxor behavior of Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3–BaBi4Ti4O15 ceramics by tape casting

Plate-like BaBi₄Ti₄O₁₅ powders were used to fabricate 0.952[Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃]–0.048BaBi₄Ti₄O₁₅(abbr. BZCT-BBT) ceramics by tape casting. The microstructure and dielectric relaxor behaviors of BZCT-BBT ceramics were investigated. BZCT-BBT ceramics can be sintered well at 1,100?°C and mainly consisted of tetragonal perovskite phase and BaBi₄Ti₄O₁₅ (abbr. BBT) phase. The lattice constants decrease as the sintering temperature increases due to substitution of Bi³⁺ for the A-site atoms of the perovskite structure. There is no obvious difference between the structure in the perpendicular and parallel directions, however, an evident difference of dielectric properties in the two directions is observed. Comparing with Ba(Zr_0.2Ti_0.8)O₃–(Ba_0.7Ca_0.3)TiO₃(abbr. BZCT) ceramics, BZCT-BBT ceramics show obvious relaxor characteristics which are evidenced by the degree of diffuseness γ calculated using the modified Curie–Weiss law. Meanwhile, the addition of BBT decreases T_m, which results from the decrease of grain size. The reduction of ε_m is mainly caused by phase structure deviation from the coexisting rhombohedral and tetragonal structure to single tetragonal.