水热法制备钛酸铋钠粉体及其生长机理研究

以钛酸四丁酯Ti(OC4H9)4和五水硝酸铋Bi(NO3)3·5H2O为原料,NaOH为矿化剂,通过水热法制备钛酸铋钠(Na0.5Bi0.5TiO3)粉体.通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)对反应制备的粉体进行物相分析.结果表明,反应温度、反应时间及矿化剂浓度均是影响钛酸铋钠粉体制备的关键因素.利用JMA方程对其进行动力学计算分析,结果表明,在反应温度为120～ 180℃时,NBT颗粒的Avrami指数n随温度的升高而减小,而反应速率k则相反,反应活化能Ea为50.14 kJ·mol-1.     

立方相Na_(1/2)Bi_(1/2)TiO_3和K_(1/2)Bi_(1/2)TiO_3的电子结构和结构不稳定性的第一性原理比较研究

采用基于密度泛函理论的第一性原理方法比较研究了Na1/2Bi1/2TiO3和K1/2Bi1/2TiO3的电子结构、离子位移势能面和Γ声子等性质.结果表明,Na1/2Bi1/2TiO3和K1/2Bi1/2TiO3的电子结构很相似,价带由O 2p电子态主导并包含部分Ti 3d和Bi 6p电子态,导带低能部分由Ti 3d空轨道构成;K取代Na后其Ti—O和Bi—O键的键强略有增加.两者的离子位移势能面也很接近,O离子的偏心位移对结构不稳定性起主导作用,且K取代Na后其作用增强.Γ声子都存在3个软模,分析表明软模主要来自O6基团的振动,K取代Na后A2u软模发生硬化.     

Electronic and Optical Properties of KNbO3,NaNbO3 and K0.5 Na0.5 NbO3 in Paraelectric Cubic Phase：a Comparative First-principles Study

The structural,electronic and optical properties of KNbO 3 (KN),NaNbO3(NN)and K05 Na0.5NbO3(KNN) in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density functional theory (DFT).The calculated electronic structures of the three crystals show similar features in the valence bands and the lower conduction bands.However,the structures in higher conduction bands differ markedly due to the effect of Na and K atoms.The calculated optical properties reveal that the features of optical spectrum at low energy are dominated by the transitions from O2p valence bands to Nb 4d conduction bands and those at high energy are related to the transitions to K 4s4p and/or Na 3s3p states.Moreover,the optical constants of KNN are approximately the average of KN and NN at high energy.Therefore,the optical properties of KNN in high energy region can probably be altered by changing the ratio of Na/K.     

(Ba0.85Ca0.15)(Ti1-xZrx)O3无铅压电陶瓷的性能研究

采用固相法制备了(Ba0.85Ca0.15)(Ti1-xZrx)O3(BCTZ)无铅压电陶瓷,研究Zr含量(x=0～0.15)对BCTZ陶瓷微观结构和电性能的影响。结果表明:所有样品均具有纯的钙钛矿结构;随Zr含量的增加,室温下样品逐渐由四方相向三方相转变,在0.05相似文献   

Ferrimagnetism and abnormal spin lattice coupling in dilute magnetic ferroelectric (Bi0.46 Na0.46 Ba0.08)TiO3:Co

We have investigated the low-temperature magnetism and spin-lattice coupling in (Bi 0.46 Na 0.46 Ba 0.08)TiO 3:Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics.It is revealed that the as-prepared (Bi 0.46 Na 0.46 Ba 0.08)TiO 3:Co at Co content of 20%～30% exhibits fascinating ferrimagnetism which is robust against magnetic field,the abnormal spin-lattice coupling characterized by a negative magnetostriction effect;and the suppressed magnetic moment within the temperature range of 30 K～50 K is identified.These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin-lattice coupling effect.Finally,the ferroelectric and magnetodielectric properties are also discussed.     

Na_(0.5)Bi_(0.5)TiO_3-K_(0.5)Na_(0.5)NbO_3无铅陶瓷介电性能研究

采用固相反应法制备了(1-x)Na0.5Bi0.5TiO3-K0.5Na0.5NbO3体系陶瓷,研究了KNN含量对Na0.5Bi0.5TiO3-xK0.5Na0.5NbO3陶瓷的晶体结构、显微结构和介电性能的影响。XRD分析结果表明,KNN进入NBT形成固溶体,该体系陶瓷均为钙钛矿结构。扫描电镜分析显示KNN的引入有利于细化晶粒,提高陶瓷致密度。测试了样品在不同频率(1 kHz,10 kHz,100 kHz,1 MHz)下的的介电温谱(室温~500℃),结果表明随着KNN含量的增加,介电峰逐渐变宽,弛豫性逐渐增强,铁电-反铁电相变温度Td和反铁电-顺电相变Tm都明显降低,当x≥0.25时,Td降至室温或更低;室温(1 kHz)下,KNN和NBT相对介电常数分别为675和575,而KNN和NBT形成的固溶体介电常数明显增大,当x=0.25时,达到最大值εr=1653。在NBT中掺入KNN得到了介电峰明显宽化、在较宽温度范围内具有低电容温度系数的致密弛豫铁电体。     

单分散钛酸锶纳米晶体的形成机理

采用水热法,利用乙醇和水的混合溶剂合成了单分散钛酸锶纳米晶体.X射线衍射(XRD)结果显示该晶体为立方相,延长反应时间其结晶性增强.扫描电子显微镜(SEM)、透射电子显微镜(TEM)结果显示样品为70 nm左右的均匀立方块晶体.利用SEM、TEM、高分辨透射电子显微镜(HRTEM)和电子衍射(ED)谱研究了该纳米晶体的生长过程,结果表明：前驱体经过扩散反应生成钛酸锶晶核,晶核之间由于定向生长作用而团聚连接形成颗粒球,最后颗粒球在缓慢的奥斯特瓦尔德熟化作用下转化为钛酸锶晶体.这一“扩散反应定向生长奥斯特瓦尔德熟化”的生长过程揭示了钛酸锶纳米晶体的生长机理.利用Johnson-Mehl-Avrami(JMA)方程模拟证实了其初始阶段的扩散反应机理,并得出反应活化能为15.79 kJ·mol^-1.     

(1-x)Bi4Ti3O12-xSrBi2Nb2O9铋层状铁电陶瓷结构与性能研究

采用传统固相法制备了(1-x)Bi4Ti3 O12-xSrBi2 Nb2 O9(BIT-SBN,x=0,0.025,0.050,0.100,0.150,0.200)铋层状无铅压电陶瓷.系统研究了SrBi2 Nb2 O9掺杂对Bi4Ti3 O12基陶瓷物相结构、微观结构以及jie电性能的影响.结果表明:所有陶瓷样品均为单一的铋层状结构;当SBN掺量为0.100时,样品具有最佳的电性能:d33=21 pC/N,相对密度ρ =98.1;,机电耦合系数kp=8.26;,εr=220,介电损耗tanδ =0.29;,剩余极化强度Pr=9.128 μC/cm2,Tc=594℃.同时,SBN的引入增强了样品的抗老化性和热稳定性.