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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. 相似文献
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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。 相似文献
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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. 相似文献
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Ferrimagnetism and abnormal spin lattice coupling in dilute magnetic ferroelectric (Bi0.46 Na0.46 Ba0.08)TiO3:Co 下载免费PDF全文
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. 相似文献
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(1-4x)NBT-3xKBT-xBT系压电陶瓷电性能研究 总被引:1,自引:1,他引:0
采用传统固相法制备了(1-4x)NBT-3xKBT-xBT(x=0.020~0.035)体系压电陶瓷。采用XRD分析发现该体系陶瓷都能形成单一的钙钛矿型固溶体,并在0.025≤x≤0.032范围内具有三方和四方共存结构,为该体系的准同型相界。当x=0.028时,d33=162pC/N,Qm=203.29,kp=0.234。电滞回线分析表明,(1-4x)NBT-3xKBT-xBT体系陶瓷随着KBT和BT含量的增加具有从铁电体向反铁电体转变的趋势。 相似文献
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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。 相似文献