SYNTHESIS AND X-RAY POWDER STUDY OF A NEW COMPOUND:Ba_6Ti_7Nb_9O_(42)

A new compound Ba6Ti7Nb9O42 was prepared for the first time by solid state reaction in BaO-TiO2-Nb2O5, ternary system. The X-ray powder diffraction data of the title compound was determined. Ba6Ti7Nb9O42 crystallizes in the hexagonal system -with unit cell parameters a=9.0527(4) A,c=11.790(1) A,and space group P63/mcm(193),z=1. The calculated and measured densities are 5. 293 g/cm3 and 5.285 g/cm3, respectively.     

水热法制备Ba_5Nb_4O_(15)纳米粉体

采用两步-水热法制备Ba5Nb4O15纳米粉体,研究矿化剂浓度、水热合成温度以及保温时间等因素对产物相组成的影响。利用X射线衍射分析样品相组成,通过Scherer公式计算所的粉体晶粒尺寸。X射线衍射结果表明,水热法合成Ba5Nb4O15单相的工艺条件为:Ba∶Nb=2∶1、碱浓度为2.0mol/L、水热反应240℃/48h,所得粉体晶粒尺寸约35nm。     

STRUCTURAL AND FERROELECTRIC PROPERTIES OF A NEW NIOBATE : Sr6FeNb9O30

A new niobate Sr_6FeNb_9O_(30) was synthesized in the ternary system SrO-Fe_2O_3-Nb_2O_5 for the first time. The crystal structure was determined by X-ray diffraction and dielectric measurement, and it belongs to orthorhombic tungsten bronze structure at room temperature with unit cell parameters a=1.7554(1) nm, b=1.7534 (1) nm, c=0.77870 (6) nm. Dielectric constants measurement show that Sr_6FeNb_9O_(30) has two phase transitions, paraelectric to ferroelectric at 185C and ferroelectric to ferroelastic at 70C.     

Synthesis and Characteristic of a New Niobate:Ba_5NaCo_0.5Nb_9.5O_30

A new niobate crystal was synthesized for the first time in BaO-Na2O-Co2O3 -Nb2O5 system by solid state reaction and the flux method. The new compound was studied by X-ray diffraction, electron probe. N-ray microanalysis, chemical analysis and SEM. The result of the X-ray diffraction shows that Ba5 NaCo0.5 Nb9.5 OK) belongs to tetragonal tungsten bronze structure with space group P4bm( 100) and lattice parameters a = b = 12.4453(2) A, c = 3. 9770 (3) A and Z = 1. The structure of the compound is different from that of Ba4Na2Nb10O30     

Synthesis and Dielectric Properties of New Niobate BiTi3Nb7O30

A new niobate Ba5 BiTi3Nb7O30 was synthesized by the solid-state reaction. It was characterized by X-ray diffraction and dielectric constant measurements. The results show that Ba5BiTi3Nb7O30 is paraelectric at room temperature and belongs to tetragonal 4/ mmm symmetry with unit cell parameters a = 1.25020 nm, c =0.39704 nm. Ba5BiTi3Nb7O30 has only one phase transition, paraelectric to ferroelectric, below 0℃.     

新化合物Sr_6CrNb_9O_(30)的合成及其结晶化学研究

在 Sr O- Nb2 O5- Cr2 O3 三元系统中 ,首次合成了新化合物 Sr6Cr Nb9O3 0 ,通过光学显微镜、化学分析、透射电镜、电子探针、X- ray衍射等手段对该化合物进行了研究 ,得到了晶体粉晶衍射数据 ,晶胞参数 a=b=1.75 0 8nm,c=0 .7748nm,晶体属正交晶系 ,空间群为 Cmm2 ,该化合物晶体具有钨青铜超结构     

SYNTHESIS AND CRYSTAL STRUCTURE OF A NEW COMPOUND Sr6Sn2Nb8O30

A new compound Sr6Sn2Nb8O30 was found in the ternary system of SrO-SnO2-Nb2O5. The transparent colorless crystal with needle-like shape can be grown by flux method. The crystal structure of new compound was determined by X-ray diffraction, and its belongs to tungsten bronze structure. Sr6Sn2Nb8O30 crystallizes in orthorhombic system with unit cell parameters a= 17. 579 (DA,6= 17. 509(DA,c=7. 7880(5)A,Z = 4 and space group Cmm2.     

Preparation,structure and dielectric properties of tungsten bronze ferroelectrics in SrO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were investigated.Both ceramics displayed weak frequency dependence in room temperature dielectric constant,which decreased from 125 to 118 for Sr4Eu2Ti4Nb6O30,from 206 to 195 for Sr5EuTi3Nb7O30 in the frequency range of 10 kHz to 1 MHz.The present ceramics showed a diffuse ferroelectric phase transition.The frequency independent transition temperature (Tm) indicated the above compounds had no relaxor property.The diffuseness (γ) was 1.45 and 1.64 for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.The weak ferroelectric of the present materials are indicated from the P-E hysteresis loops,and a small 2Pr of 0.596 μC/cm2 and 0.068 μC/cm2 were observed for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.     

Crystal Structure of a New Compound :Na_(2.1)Ba_(0.9)Cu_(0.1)Nb_(4.9)O_(14.3)

Single crystal of a new compound Na2.1Ba0.9Cu0.1Nb4.9O14.3 was synthesised for the first time. The crystal structure has been determined by single crystal X-ray diffraction and the final R value is 0. 0559. The compound crystallizes in a tetragonal unit cell [a = 12. 442(3) A and c = 3. 954 A ]with space growp P4/mbm and Z=2. The compound is in tetragonal tungsten-bronze type structure but some oxygen vacancies exist in the structure. The structure of the compound consists of NbO6 octahedra and octahedra (Nb, Cu)O6 to form triangle, quadrilateral and pentagonal tunnels. The quadrilateral tunnels are occupied by Na atoms. More than 1/2 pentagonal tunnels are occupied by Na atoms and less than 1/2 that are occupied by Ba atoms. Cu2 replaces Nb5 to form different-valence isomorpism.     

KTa0.5Nb0.5O3电子结构的第一性原理研究

用全电势线性缀加平面波法（FLAPW）计算了KTa0.5Nb0.5O3铁电相和顺电相的态密度、能带结构。通过对两相态密度的对比分析发现，在铁电相，钽原子的d电子和氧原子的2p电子以及铌原子d电子与氧原子的2p电子之间存在强烈的轨道杂化，对能带的分析也得出同样的结论，这种轨道杂化对KTa0.5Nb0.5O3铁电性的稳定有着重要的意义。钽原子在四方铁电体KTa1-xNbxO3中的作用与在纯钽酸钾中的作用有明显的差别。     

纳米晶Ba（Zr0．2Ti0．8）O3薄膜的外延生长与介电特性

用脉冲激光沉积工艺在半导体（001）SrTiO3：ω（Nb）=1．0％单晶基片上,外延生长出Ba（Zr0.2Ti0.8）O3（简称BZT）介电薄膜．在650℃原位退火10min,薄膜为（001）外延生长的晶粒．薄膜的晶化特征与表面形貌用薄膜X-ray衍射仪和原子力显微镜测量完成．BZT薄膜（002）峰的半峰宽只有0．72°,说明薄膜晶化良好;薄膜的平均晶粒为90nm,表面均方根粗糙度为4．3nm,说明薄膜表面平整．在室温、100kHz和500kV／cm条件下,BZT的最大介电常数和调谐百分率分别达到317和65％．     

SYNTHESIS AND CHARACTERIZATION OF A NEW NIOBATE: Sr6Ti7Nb9O42

A new niobate Sr_6Ti_7Nb_9O_(42) was synthesized for the first time by solid state reaction in SrO-TiO_2Nb_2O_5 ternary system. The new compound was characterized by EPMA, XRD, SEM and DTA. The X-ray owder diffraction data of Sr_6Ti_7Nb_9O_(42) were firstly reported in the paper. Sr_6Ti_7Nb_9O_(42) crystallizes the hexagonal system with unit cell parameters a=8.9991(4)(?), c=11.5118(9)(?), and space group P6_3/mcm(193), z=1. The calculated and measured densities are 4.783 g/cm~3 and 4.764 g/cm~3, respectively.     

A new sol-gel process for preparing Ba（Mg1／3Nb2／3）O3 nanopowders

Commercially available niobium (V) oxide [Nb2O5], with barium acetate [Ba(CH3COO)2] and magnesium acetate [Mg(CH3COO)2·4H2O] was used as the starting material in the sol-gel process for preparing Ba(Mg1/3Nb2/3)O3 (BMN) nanopowders. At first, Nb2O5 reacted with melting sodium hydroxide and transformed into dispersible oxide. The resulting glassy substance after cooling was dispersed and washed several times in distilled water to remove the Na ions. The as-prepared colloidal Nb2O5·nH2O was subsequently mixed with acetic solution of barium acetate and magnesium acetate according to the required molar proportions and followed by gelation. The ultrafine BMN powders were finally obtained after heat-treating the gel at 820℃ for 1 h, and the as-sintered nanoceramics revealed a high relative density of 98.2%, and a high microwave Q-factor, of 10397 at 1.45GHz.     

High Dielectric Constant and Low-loss Dielectric Ceramies of Sr5LnTi3Ta7O3o （Ln= La,Nd, Sm and Y）

Polycrystalline Sr5LnTi3Ta7O30 （Ln=La, Nd, Sm and Y） ceramics were prepared as single-phase materials through conventional solid-state ceramics method. The structure was characterized by X-ray diffraction method and scanning electron microscopy （SEM）. The dielectric properties were measured from room temperature to 400℃. All compounds are paraelectric phases adopting the filled tetragonal tungsten bronze （TB） structure at room temperature. At 1 MHz their dielectric constant （ετ） varied from 109 to 139, dielectric loss changed from 0.003 3 to 0.005 8, and the temperature coefficients of the dielectric constant （τε） moved from -710 to -880×10^-6℃^-1.     

Li_6SrLa_2Nb_2O_(12):Pr~(3+)的发光性质

用高温固相法制备了Li6SrLa2Nb2O12:Pr3+,并通过X射线衍射仪及荧光光谱仪分析了其结构和发光性质.结果表明:激发光谱出现NbO7-6吸收和Pr3+的4f→4f5d激发跃迁;发射光谱出现强的绿光发射,其峰值位于491nm,同时在610nm处有弱的红光发射,这两种发射分别属于Pr3+的3P0→3 H4和1 D2→3 H4的电荷跃迁.Pr3+在Li6SrLa2Nb2O12:Pr3+中的最佳掺杂浓度为0.5mol%.     

Effect of Li content on the microstructure and properties of lead-free piezoelectric （K0.5Na0.5）1-xLixNbO3 ceramics prepared by SPS

Lead-free piezoelectric （K0.5sNa0.5）1-xLixNbO3 （x = 0at%-20at%） ceramics were synthesized by spark plasma sintering （SPS） at low temperature and the effects of LiNbO3 addition on its crystal structure and properties were also studied. When the Li content was less than 6at%, a single proveskite phase with the similar structure of （K0.5Na0.5）NbO3 was formed; and a secondary phase with K3Li2Nb5O15 structure was observed in the 6at% 〈 x 〈 20at% compositional range. Furthermore, LiNbO3 existed as the third phase when the Li content was higher than 8at%. The grain sizes increased from 200-500 nm to 5-8 μm when the K3Li2Nb5O15 and LiNbO3 like phases were formed. With increasing Li content, the relative density of the ceramics first decreased from 97% to 93% and then kept constant. The piezoelectric coefficient d33, dielectric constant, and planner electromechanical coupling factor exhibited a decreasing tendency with increasing Li content because of the decrease in density and the formation of the secondary phase such as K3Li2Nb5O15 and LiNbO3. The formation of dense microstructure with a single phase is necessary in improving the properties of the （K0.5Na0.5）1-xLixNbO3 ceramics.     

铌钴共掺杂钛酸钡陶瓷的介电温度稳定性的研究

采用X射线衍射(XRD)、拉曼光谱(RS)、原子力显微镜(AFM)以及介电温谱(DTC)研究BaTiO3-xNb2O5-0.005Co2O3(x=0.02,0.04,0.08)系统中Nb含量变化对陶瓷的结构及介电温度稳定性的影响.结果表明:增加Nb含量将增强介电陶瓷的温度稳定性,但介电常数降低.Nb含量在4%以上时NC陶瓷满足X7R介电指标.     

新型五硼酸盐的熔盐合成及结构表征

通过低温熔盐法合成了一种新型五硼酸盐RbB5O7（OH）2·H20,单晶X射线衍射结果证明该化合物属单斜晶系,P2／c空间群,α=0．7640（2）nm,b=0．9019（3）nm,c=1．0833（3）nm,β=103．681（5）°,V=0．7252（4）nm^3,Z=2．结构中BO3,BO2（OH）2,BO4基团形成的[B5O7（OH）2]之字链结构与RbO＋相连构成九面体-四面体空间骨架,水分子靠近之字链结构通道内侧,起到稳定骨架的作用．同时通过X粉晶衍射、红外光谱、热重等对化合物进行了表征．     

Synthesis and X-ray Powder Diffraction Characterization of A New Niobate Crystal Ba_4Na_2VNb_9O(30)

A new niobate crystal Ba4Na2 VNb9O30 was synthesized in BaO-Na2O-V2O5-Nb2O5 system for the first time. Its shape, optical properties , melting point and chemical stability were studied. X - ray powder diffraction study determined that this compound assumes a tetragonal tungsten bronze structure with space group P4bm(100) and lattice parameters a = b= 12.4275(2),e=3.970(3). The new compound may be one kind of photorefractive crystals.     

SYNTHESIS AND CHARACTERIZATION OF A NEW COMPOUND:K6Ti0.67Nb15.33O42

A new compound K6Ti0.67Nb15.33O42 was prepared for the first time by solid state reaction in K2O-Ni2O3-Nb2O5 ternary system. The new compound was characterized by electron probe, X-ray powder diffraction and DTA. The result of X-ray powder diffraction shows that K6Ti0.67Nb15.33O42 crystallizes the hexagonal system with unit cell parameters a = 9. 1341(5) A ,c=12. 090(1)A . and space group P62/mcm(193 ).