Bi4Ti3O12掺杂对(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7陶瓷结构与介电性能的影响

研究了Bi4Ti3O12掺杂对(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7(BZN)陶瓷烧结特性、相结构和介电性能的影响.采用传统的固相反应法制备样品,X射线衍射技术分析相结构,SEM观察表面形貌.结果表明,Bi4Ti3O12掺杂能有效地促进烧结,提高介电常数ε,降低介电损耗tgδ,优化介电频率温度系数αε.1000℃烧结8%(摩尔分数) Bi4Ti3O12掺杂的BZN陶瓷具有较好的介电性能ε=192,tgδ= 4.21×10-4,αε=-3.37×10-4/℃.     

MnO2对Ba(Mg1/3Nb2/3)O3微观结构和微波介电性能的影响

研究了MnO2助烧剂对Ba(Mg1/3Nb2/3)O3陶瓷的微观结构和微波介电性能.MnO2可以有效地使Ba(Mg1/3Nb2/3)O3陶瓷的致密化温度由1550℃降低到1400℃左右.随MnO2掺量的增加,Ba(Mg1/3Nb2/3)O3陶瓷的12超晶格衍射峰的强度减弱,但是没有第二相出现.1400℃烧结4h陶瓷的晶粒尺寸在1.5μm左右.MnO2的掺入改善了Ba(Mg1/3Nb2/3)O3陶瓷的微波介电性能,MnO2掺量为1%mol的Ba(Mg1/3Nb2/3)O3陶瓷具有最好的微波介电性能εr≈31.5,Qf=68000,τf=3.11×10-5/℃,这可归功于陶瓷具有相当高的相对密度.     

Bi2O3掺杂对Mg4Nb2O9陶瓷的微结构及微波介电性能的影响

采用固相反应法制备了Mg4Nb2O9基微波介质陶瓷,研究了Bi2O3掺杂对Mg4Nb2O9陶瓷烧结行为、相结构、显微结构及微波介电性能的影响。实验结果表明:Mg4Nb2O9陶瓷烧结温度随Bi2O3掺杂量的增加而减小,添加2.0wt%Bi2O3,烧结温度从1350℃降低至1175℃;随Bi2O3添加量从0.0wt%增大到3.0wt%,最强峰(104)晶面间距d值由2.756nm增大至2.769nm;Mg4Nb2O9陶瓷的微波介电性能随Bi2O3掺杂量增加而变化;掺杂2.0wt%Bi2O3的Mg4Nb2O9陶瓷在1175℃保温2小时烧结,获得亚微米级陶瓷,且具有最佳的微波介电性能,εr为12.58,Q×f为71949.74GHz。     

Na-Sn掺杂Bi2O3-ZnO-Nb2O5陶瓷的性能

研究了Na+替代Bi3+、Sn4+替代Nb5+对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结特性、显微结构和介电性能的影响.结果表明,替代后样品的烧结温度从1000℃降低到860℃;在-30～130℃样品出现明显的介电弛豫现象;弛豫激活能在0.3eV左右.用缺陷偶极子和晶格畸变对Na-Sn掺杂Bi2(Zn1/3Nb2/3)2O7的介电弛豫现象进行了解释.     

(1-y)Ca1-xLa2x/3 TiO3-yCa(Mg1/3 Nb2/3)O3系陶瓷的缺位结构与微波介电性能研究

采用固相合成法制备了(1-y)Ca1-xLa2x/3 TiO3-yCa(Mg1/3Nb2/3)O3系列固溶体陶瓷材料,研究了该体系微波介电性能与微观结构的关系.研究结果表明:当体系组成为0.5Cao6Lao267 TiO3-0.5Ca(Mg1/3Nb2/3)O3时,在1400℃下烧结保温4小时所得到材料的微波介电性能最佳:εr=55,Q×f值=45000GHz(7.6GHz下),τf=0.04×10-6/℃.同时还探讨了三价阳离子La3 固溶时产生的A点缺陷Vca2 对固溶体结构及微波介电性能的影响.     

掺ZBS玻璃低温烧结ZnNb2O6微波介质陶瓷的研究

研究了ZnO-B2 O3-SiO2(ZBS)玻璃料对ZnNb2O6微波介质陶瓷烧结特性和介电性能的影响.结果表明,ZBS玻璃料形成的液相加速了颗粒间的传质,促进了烧结,能使ZnNb2O6陶瓷的烧结温度有效地降低至950℃.随着ZBS含量的增加,样品中出现了第二相,且气孔被包裹在晶粒内部难以逃脱出来,导致样品的缺陷和损耗增加,从而降低介电性能.掺杂1%ZBS的ZnNb2O6陶瓷在950℃保温4h,能获得优异的综合介电性能:ε=23.56、Q·f=18482GHz、τf=-28.8×10￣6/℃.     

掺杂Bi_2Ti_2O_7对Y_2O_3-2TiO_2系微波介质陶瓷材料性能的影响

目前国内外对εr范围在40～80左右的中介电常数微波介质陶瓷体系的研究还很缺乏。为适应现代微波通讯技术发展需求,本实验研究开发了新型中介电常数Y2O3-2TiO2系微波介质陶瓷,并在此基础上添加Bi2Ti2O7陶瓷粉料进行复相掺杂。利用网络分析仪,阻抗分析仪,XRD,SEM等方法,本文重点研究了不同Bi2Ti2O7掺杂量对Y2O3-2TiO2系微波介质陶瓷材料烧结性能和介电性能的影响。通过分析发现适量掺杂能够有效降低材料的烧结温度,并使材料致密化。同时由于Bi3+置换主晶相中的Y3+形成了固溶体,材料主晶相为烧绿石结构并未改变。当添加质量分数为8wt%时获得介电性能较好的陶瓷材料,烧结温度从未掺杂的1460℃降低到1320℃。在1M下:εr≈62.14,tanδ≈1.22×10-3,微波频率(4.55GHz)下εr≈62.85,Q.f=4122.8GHz,τf=-7ppm/℃。     

B2O3对BaO-Sm2O3-TiO2微波介质陶瓷性能的影响

为了满足微波器件小型化的需要,开发高介电常数的低温烧结微波介质材料成为一种趋势.采用复合掺杂低熔点氧化物来降低BaO-Sm2O3-TiO2系(BST)微波介质陶瓷的烧结温度,通过X射线衍射和扫描电子显微镜分析其物相组成和显微结构,用阻抗分析仪测量了陶瓷材料的介电性能.结果表明:在Ba4(Sm1-0.15Bi0.15)28/3Ti18O54的基质陶瓷材料中,复合掺杂3%的ZnO和2%的B2O3时,其烧结温度为1060℃,得到的BST微波介质陶瓷的介电性能为:εr≈64,tanδ≈1.2×10-3,τf=-8.3×10-5/℃.     

CaTiO3 对(1-x)ZnAl2O4-xMg2TiO4(x=0.21)微波介质陶瓷结构和性能的影响

利用常规固相法制备了ZnAl2O4-Mg2TiO4-CaTiO3陶瓷,研究了CaTiO3对其相成分、微观组织结构和微波介电性能的影响规律. 结果表明,CaTiO3能有效地改善(1-x)ZnAl2O4-xMg2TiO4(x=0.21)材料的烧结性能,使其致密化温度降低150℃. ZnAl2O4-Mg2TiO4-CaTiO3陶瓷体系中包括ZnAl2O4基尖晶石相、CaTiO3、MgTi2O5和Zn2Ti3O8相,当烧结温度高于1400℃时,Zn2Ti3O8相消失. 随着CaTiO3含量的增加,体系中CaTiO3相含量增加而MgTi2O5相含量减少,且CaTiO3具有显著地调节谐振频率温度系数的作用. 当在(1-x)ZnAl2O4-xMg2TiO4(x=0.21)体系中掺入6mol%的CaTiO3添加剂时,经1400℃烧结后能获得温度稳定性好的微波介质陶瓷材料,其微波介电性能为:εr=11.8,Q*f=88080GHz,τf=-7.8×10-6/℃.     

CO3O4掺杂Mg2SiO4陶瓷介电性能的研究

采用固相反应法制备了Co3O4掺杂Mg2SiO4微波介质陶瓷,研究Co2+离子掺杂对Mg2SiO4陶瓷烧结特性、相组成和介电性能的影响.结果表明:Co2+可以完全取代Mg2+固溶在Mg2 SiO4晶体中形成(Cox Mg1-x)2SiO4固溶体,通过调整加入的Co3O4的摩尔量可以获得介电性能优良的微波陶瓷.当x=0.025时,在1250℃下保温3h,( Co0.025Mg0.975)2 SiO4陶瓷具有良好的介电性能为:εr=7.7,Q=8850(1.8MHz),电容温度系数为50.4×10-6/℃.     

Neutron and X-ray powder diffraction studies of the oxynitrides SrW(O,N)3, Ba3W2(O,N)8 and Ba3Mo2(O,N)8

Oxynitrides of composition SrW(O,N)₃, Ba₃W₂(O,N)₈ and Ba₃Mo₂(O,N)₈ have been prepared by the ammonolysis of stoichiometric mixtures of oxides and carbonates. Combined Rietveld refinements of powder neutron and powder X-ray diffraction data have allowed the structure of each to be determined. SrW(O,N)₃ was found to have a cubic Perovskite structure whereas Ba₃W₂(O,N)₈ and Ba₃Mo₂(O,N)₈ have a layered hexagonal structure. In the hexagonal structures the oxygen and nitrogen atoms are distributed almost randomly over two sites in the unit cell producing 4-fold co-ordination to tungsten and molybdenum, a distorted octahedral co-ordination to one barium site and a 10-fold co-ordination to the other.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Hydrothermal Crystallization in the Systems Nd2O3(Nd(NO3)3 ⋅ 6H2O)-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaCl, NH4Cl, NaHCO3, KHCO3, Na2CO3 + NaCl, Na2CO3 + NH4Cl, Na2CO3 + CO(NH2)2)

Hydrothermal crystallization in the systems Nd₂O₃(Nd(NO₃)₃ ? 6H₂O)-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaCl, NH₄Cl, NaHCO₃, KHCO₃, Na₂CO₃ + NaCl, Na₂CO₃ + NH₄Cl, Na₂CO₃ + CO(NH₂)₂) was studied in the range 400–480°C. All of the precipitates were found to contain crystalline NdOHCO₃, NaNd(CO₃)₂, and Nd₂(OH)₄CO₃. The lattice parameters of NdOHCO₃ were refined, and a detailed scheme for its thermal decomposition was proposed.     

Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

The process and nature of structural ordering and the factors that influence them have been investigated in the microwave dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy. The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

纳米(ZnO,Al2O3)复合掺杂对3Y2O3-ZrO2材料电性能的影响

以3Y2O3—ZrO2纳米粉和ZnO，A12O3纳米粉为原料，采用交流阻抗谱技术对掺少量ZnO和A12O3的3Y2O3—ZrO2烧结陶瓷进行电性能研究。研究表明：少量纳米ZnO掺杂降低了3Y2O3—ZrO2的电导率，但随着掺人量的增加，电导率开始回升。在ZnO掺杂样品中加入少量纳米A12O3进行复合第二相掺杂，结果提高了3Y2O3—ZrO2材料的电导率。同时少量A12O3的掺人降低了晶粒电导活化能，使得晶粒电导率增加。     

Combustion Synthesis of Glass (B2O3-Al2O3-MgO)-Ceramic (TiB2) Composites

The combustion synthesis, or self-propagating high temperature synthesis (SHS), technique has been used to produce glass ceramic composites that have a glass matrix based on B₂O₃-MgO-Al₂O₃and a crystalline ceramic phase of TiB₂. Conditions for producing glassy materials by the SHS technique are discussed and the thermodynamics of these combustion reactions are analyzed. The combustion characteristics, i.e., ignition energy, combustion temperature, and wave velocity have been determined. Green density of the pellets had a significant effect on the combustion characteristics. Green pellets with low density were used to reduce heat loss, thus enabling the synthesis of those compositions having low adiabatic temperatures. The glass-forming region of these SHS glasses was found to be in relatively good agreement with that of samples produced by the traditional furnace-melting method.