高温KNbO3熔液内速度场和温度场的实验研究及其数字模拟分析

在重力对流作用的情况下，本文对实验所用的铂金坩埚中的高温熔液内的速度分布和温度分布进行了数字模拟研究。结果表明：借助实验边界条件和Boussinesq近似，铌酸钾高温熔液中的速度分布及温度分 的数字模拟结果与实验结果基本吻合，流体运动的轨迹与实验示踪粒子轨迹也基本一致。     

对流效应和溶质浓度对KNbO3晶体界面形貌稳定性的影响

研究了在不同对流形态对KNbO3晶体生长形貌的影响。在温度梯度较小的扩散-平流区域,晶体以枝蔓晶的形态生长;而在温度梯度的较大的扩散-对流区域,生长出的晶体呈现光滑晶面。通过测定不同区域KNbO3晶体界面附近的溶质浓度分布,从对流效应降低晶体界面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算相一致。同时解释了扩散-对流区域的晶体尺寸大于扩散-平流区域的晶体尺寸的原因。观察并定性地解释了不同溶质浓度KNbO3形成不同的界面非稳定形貌,当KNbO3重量百分比为20wt%时形成骸晶,30wt%时形成枝蔓晶。     

Mg:Sc:Fe:LiNbO_3晶体缺陷结构和全息存储性能

采用提拉法,从Li/Nb变化(0.94,1.05,1.20,1.38)的熔体中生长出Mg:Sc:Fe:LiNbO_3晶体。Li/Nb=1.05的晶体OH~-振动吸收峰在3504cm~(-1)处出现的主吸收峰,且在3466cm~(-1)、3481m~(-1)处有两附加峰。Li/Nb=1.38的晶体OH~-振动吸收峰在3535 cm~(-1)处出现附加吸收峰。红外光谱结果表示Li/Nb=1.05的晶体是近化学剂量比的,且Sc掺质优先于Mg掺质达到阈值浓度。采用透射光斑畸变法测得Mg:Sc:Fe:LiNbO_3晶体(Li/Nb=1.05)的抗光损伤能力为2.0×10~4W/cm~2,比Fe:LiNbO_3提高了三个数量级。采用波长为632.8nm的He—Ne激光器作为光源,通过二波耦合方法测试晶体全息存储性能。实验结果表明:随着Li/Nb的增加,晶体的写入时间缩短,晶体的衍射效率降低,光折变灵敏度增加,动态范围减少。在一系列晶体中,Mg:Sc:Fe:LiNbO_3晶体(Li/Nb=1.05)更加适合作为全息存储介质。     

LiNbO3薄膜的研究进展

LiNbO3薄膜具有优良的压电、热释电、声光及非线性光学特性，在光电子学及集成光学等领域有许多重要应用，着重介绍LiNbO3的结构，性质与薄膜制备技术，以及在光通信领域中的应用。     

氧化还原处理对Fe:LiNbO3晶体光折变性能及热固定效果的影响

在LiNbO3中掺进Fe2O3生长了Fe:LiNbO3晶体,并对晶体进行氧化、还原处理。利用二波耦合的方法,测试了不同还原处理的Fe:LiNbO3,晶体的指数增益系数、衍射效率及响应时间。测试了三种不同处理本热固定后的显影效率,记录了全息先栅的记录、热补偿及离子衰减过程。发现不同氧化还原处理的晶体在光折变性能和热固定效果上有不同的表现。     

掺铟LiNbO3晶体抗光折变效应增强机理的研究

在LiNbO3中掺进不同浓度的抗光折光折变杂质离子In^3 ,生长In(2mol％）：LiNbO3和In(3mol％）：LiNbO3晶体。研究In:LiNbO3晶体的结构和In^3 离子在LiNbO3晶体中的占位,利用光斑变形法和全息法测试了In:LiNbO3晶体的抗光折变性能,分析了In^3 使LiNbO3晶体抗光折变效应增强的机理。     

Co^3＋—modified Surface of LiMn2O4 Spinel for its Improvementof Electrochemical Properties

Cobalt was used to modify the surface of spinel LiMn2O4 by a solution technique to produce Co^3 -modified surface material (COMSM). Cobalt was only doped into the surface of LiMn2O4 spinel. XPS(X-ray photoelectron spectroscopy) analysis confirms the valence state of Co^3 . COMSM has stable spinel structure and can prevent active materials from the corrosion of electrolyte. The ICP(inductively coupled plasma) determination of the spinel dissolution in electrolyte showed the content of Mn dissolved from COMSM was smaller than that from the pure spinel. AC impedance patterns show that the charge-transfer resistance (Rct) for COMSM is smaller than that for pure spinel. The particles of COMSM are bigger in size than those of pure spinel according to the micrographs of SEM(scanning electron microscopy). The determinations of the electrochemical characterization show that COMSM has both good cycling performance and high initial capacity of 124.1 mA/h at an average capacity loss of 0.19 mAh/g per cycle.     

铌酸钠钾基无铅压电陶瓷制备技术新进展

碱金属铌酸盐系无铅压电陶瓷以其优越的压电性能和较高居里温度倍受关注.结合目前有关KNbO3-NaNbO3(KNN)基无铅压电陶瓷的报道,综述了近年来铌酸钠钾基无铅压电陶瓷在粉体制备、陶瓷的成型、烧结以及晶粒取向等制备技术研究的新进展,并从不同方面展望了今后铌酸钠钾基无铅压电陶瓷性能研究及其制备技术上可能的进展.     

对流效应和溶质浓度对KNbO_3晶体界面形貌稳定性的影响

研究了在不同对流形态对ＫＮｂＯ３晶体生长形貌的影响．在温度梯度较小的扩散－平 流区域,晶体以枝蔓晶的形态生长;而在温度梯度较大的扩散－对流区域,生长出的晶体呈现 光滑晶面．通过测定不同区域ＫＮｂＯ３晶体界面附近的溶质浓度分布,从对流效应降低晶体界 面附近的溶质浓度分布的不均匀性的角度研究了对流效应对晶体界面形貌稳定性的影响,证明 对流效应提高了晶体界面形貌稳定性,与晶体界面弥散度的理论计算结果相一致．同时解释了 扩散－对流区域的晶体尺寸大于扩散－平流区域的晶体尺寸的原因．观察并定性地解释了不同 溶质浓度ＫＮｂＯ３形成不同的界面非稳定形貌,当 ＫＮｂＯ３重量百分比为２０ｗｔ％时形成骸晶, ３０ｗｔ％时形成枝蔓晶．     

铌酸钾钠基无铅压电陶瓷的相变特性和掺杂改性研究进展

人类社会可持续发展的要求以及一些发达国家有关电子产品无铅化法规的全面实施,近年来无铅压电陶瓷的研究与开发受到极大关注.碱金属铌酸盐系压电陶瓷以其优越的压电性能和较高居里温度受到人们高度重视.结合近年有关KNbO3-NaNbO3(KNN)基无铅压电陶瓷的报道,着重从KNN基压电陶瓷的相变特性、掺杂改性和引入第三组元等几个方面,介绍了相关研究的现状,并对KNN基压电陶瓷的发展趋势进行了展望.     

高温氧化物晶体界面非稳定性研究

设计了一套模拟实验,以获得关于晶体形态和界面非稳定性的差异的可靠数据,如高温溶液生长的骸晶和枝蔓晶．这些实验是在高温实时观察装置（ＨＩＴＩＳＯＴ）内进行的．高温溶液晶体生长实验是在环形铂金丝炉圈内进行的．炉圈直径为２ｍｍ．铂金丝既起加热又起支撑熔体的作用．选用ＫＮｂＯ_３和Ｌｉ_２Ｂ_４Ｏ_７的混合物进行晶体生长实验．在只存在扩散机制的快速生长过程中,会形成不同的晶体不完整性,如晶面凹坑、骸晶和枝蔓晶．采用淬火实验以分辨不同的ＫＮｂＯ_３晶体形态,并用扫描电镜研究Ｌｉ_２Ｂ_４Ｏ_７溶体中ＫＮｂＯ_３晶体生长的形貌．在一般情况下,当晶体在气液界面附近液相区成核时,会产生晶体界面非稳定性．导致晶体形状不稳定的溶液层的厚度为６０μｍ．通过扫描电镜观察,发现晶体在这一溶液层中由多面体晶变为枝蔓晶．骸晶和枝蔓晶的各向异性反映了ＫＮｂＯ_３的立方特性,也反映了界面非稳定性是沿［１１０］晶棱扩大的,［１１０］晶棱方向的分支证实了晶体生长形状的各向异性·形成界面非稳定性的临界尺寸为１０μｍ．与此相反,中持稳定的晶面形状是通过６０μｍ厚度以下的溶液内的晶体生长来实现的．晶体生长过程是由高温实时观察装置进行实时观察和记录的,并能观察到晶体固液     

First Observation of the Critical Size of Facets on 3He Crystals near 1 mK

We have been able to obtain the step free energies of the basic (110) and (100) facets on ³He crystals near 1 mK by using a new method in which the critical radius of facets is measured on slowly melting crystals. The critical radius is obtained by tracking optically the moment that the facet collapses. Our findings confirm that at such low temperatures the liquid–solid interface of ³He is indeed strongly coupled to the crystal lattice, as was suggested in our previous studies.     

Complementary characterization techniques for identification of ferroelectric domains in KNbO3 single crystals

KNbO₃ single crystals are often utilized for their piezoelectric and optical properties. In this study the domain configurations in as-grown single crystals were investigated using reflected light microscopy, scanning electron microscopy and atomic force microscopy. Using atomic force microscopy it was possible to image the distortion induced on the crystal surface by the domain walls and to quantify the predicted angle between (001)_pc planes across these walls for the cases of both 90° domain walls and S walls. These features can also be imaged using the other two techniques. This direct measurement of surface distortion verifies the geometrical model of domain structures, and suggests that any possible strain energy considerations are minor in predicting the surface topography in the material after phase changes from the growth temperature.     

Laser Excitation Effect on the Optical and Dielectric Properties of Ferroelectric KNbO3 Single Crystals

The effects of laser irradiation on the optical absorption (200- to 800-nm range) and dielectric properties (10²- to 10⁷-Hz range) of KNbO₃ single crystals in ferroelectric phase have been studied. All these properties are found to be reduced significantly at lower frequencies with an increase in laser irradiation time. However, the phase transition temperature remains unchanged. It is observed that the dielectric constant (K) and loss (tan ) values of KNbO₃ single crystals are decreased significantly at room temperature or at Curie temperature by laser excitation. Appreciable changes in the band gap (eV) and activation energy are also observed after laser excitation.     

微波水热法制备KNbO3粉体及其性能研究（英文）

以氢氧化钾(KOH)和五氧化二铌(Nb2O5)为原料,通过微波水热法在200℃下合成出具有不同晶相、形貌的铌酸钾粉体(KNbO3).当KOH浓度在10~14mol/L时,可以制备出纯相的KNbO3粉体.X射线衍射(XRD)、场发射扫描电镜(FESEM)和透射电镜(TEM)分析可知,KOH浓度由10mol/L增大到15mol/L时,KNbO3粉体由斜方六面体变为正交相,再转变为四方相,对应的形貌也由金字塔状变为棒状,再转变为立方状.当KOH浓度增大到15mol/L时,出现了Nb2O5杂相.常压烧结制备了KNbO3陶瓷,其介电常数达到302,介电损耗为0.023,压电常数达到80 pC/N,平面机电耦合系数为0.17,机械品质因数为70,居里温度为420℃,正交?四方相变温度为223℃.     

Photostriction of CH3NH3PbBr3 Perovskite Crystals

Organic–inorganic hybrid perovskite materials exhibit a variety of physical properties. Pronounced coupling between phonon, organic cations, and the inorganic framework suggest that these materials exhibit strong light–matter interactions. The photoinduced strain of CH₃NH₃PbBr₃ is investigated using high‐resolution and contactless in situ Raman spectroscopy. Under illumination, the material exhibits large blue shifts in its Raman spectra that indicate significant structural deformations (i.e., photostriction). From these shifts, the photostrictive coefficient of CH₃NH₃PbBr₃ is calculated as 2.08 × 10^?8 m² W^?1 at room temperature under visible light illumination. The significant photostriction of CH₃NH₃PbBr₃ is attributed to a combination of the photovoltaic effect and translational symmetry loss of the molecular configuration via strong translation–rotation coupling. Unlike CH₃NH₃PbI₃, it is noted that the photostriction of CH₃NH₃PbBr₃ is extremely stable, demonstrating no signs of optical decay for at least 30 d. These results suggest the potential of CH₃NH₃PbBr₃ for applications in next‐generation optical micro‐electromechanical devices.