沉积温度对磁控溅射BiFeO3薄膜结构和性能的影响

应用磁控溅射法在以SrRuO3 (SRO)薄膜为缓冲层的Pt/TiO2/SiO2/Si(001)基片上制备了多晶BiFeO3 (BFO)薄膜,构架了SRO/BFO/SRO异质结电容器.采用X射线衍射、铁电测试仪等研究沉积温度对BFO薄膜结构和性能的影响.X射线衍射图谱显示BFO薄膜为多晶结构.在2.5 kHz测试频率下,500℃生长的BFO薄膜呈现比较饱和的电滞回线,2Pr为145μC/cm2,矫顽场Ec为158 kV/cm,漏电流密度约为2.4×104 A/cm2.漏电机制研究表明,在低电场区,SRO/BFO/SRO电容器满足欧姆导电机制,在高电场区,满足普尔-弗兰克导电机理.实验发现:SRO/BFO/SRO电容器经过109翻转后仍具有良好的抗疲劳特性.     

不同电极对外延BiFeO3薄膜铁电性能的影响

采用磁控溅射的方法在SrRuO3/SrTiO3(001)衬底上外延生长BiFeO3薄膜,研究以不同金属或氧化物做顶电极时的铁电、铁磁性质和漏电流及其导电机制。X射线衍射图谱和Φ扫描图结果显示BiFeO3薄膜沿c轴外延生长,以Pt、Al做顶电极的薄膜剩余极化强度2Pr为68μC/cm2,生长Pt/SRO、FePt顶电极的薄膜剩余极化强度较小,2Pr为44μC/cm2,矫顽场2Ec约为370±20 kV/cm。薄膜的漏电流密度较小而且趋于饱和,在U=12 V时最大为1.94×10-3A/cm2,体传导普尔弗兰克导电为BiFeO3薄膜主要的导电机制。BFO薄膜展现出弱磁性,饱和磁化强度为9.3 emu/cm3,矫顽场为338 Oe。     

外延铁酸铋薄膜铁电性和反转特性的研究

采用磁控溅射的方法在以SrRuO3 (SRO)为底电极的(001)取向的SrTiO3基片上制备了外延BiFeO3 (BFO)薄膜,并以氧化铟锡(ITO)和金属Pt为上电极构架了ITO/BFO/SRO和Pt/BFO/SRO两种薄膜电容器,研究上电极对外延BFO薄膜铁电性和反转特性的影响.结果表明,两种薄膜电容器均体现了良好的饱和电滞回线,当测试电场为333 kV/cm时,ITO/BFO/SRO和Pt/BFO/SRO两种电容器的剩余极化强度分别为47.6 μC/cm2和56 μC/cm2,矫顽场分别为223 kV/cm和200 kV/cm.此外,两种薄膜电容器都具有良好的保持和抗疲劳特性.通过反转和非反转电流对时间的积分,可以计算出真实的极化强度.当反转电压幅值为17 V时,ITO/BFO/SRO和Pt/BFO/SRO两种电容器电流的反转时间分别为0.48 μs和0.32μs,真实极化强度的计算值约为41μC/cm2和47 μC/cm2,此计算值和铁电净极化强度的测量值符合的很好.     

SrRuO3导电层对快速退火制备Pb(Zr,Ti)O3薄膜结构和性能的影响

采用溶胶-凝胶法在Pt/Ti/SiO2/Si基片上,制备了Pt/Pb(Zr,Ti)O3(PZT)/Pt和SrRuO3(SRO)/PZT/SrRuO3(SRO)异质结电容器,并研究了快速退火条件下SRO导电层对PZT结构和性能的影响.XRD测试表明,两种结构电容器中的PZT薄膜均为钙钛矿结构,SRO/PZT/SRO、Pt/PZT/Pt均具有较好的铁电性和脉宽依赖性,5 V电压下两电容器的剩余极化强度Pr和矫顽电压Vc分别为28.3 μC/cm2、1.2 V和17.4 μC/cm2、2.1 V.在经过1010次翻转后,SRO/PZT/SRO铁电电容器疲劳特性相对于Pt/PZT/Pt电容器有了较大的改善,但SRO导电层的引入也带来了漏电流增大的问题.     

保持温度对偏轴磁控溅射法制备BiFeO3薄膜结构和性能的影响

本文采用偏轴磁控溅射方法在Pt/TiO2/SiO2/Si(111)基片上制备了多晶BiFeO3(BFO)薄膜,并构架了Pt/BFO/Pt异质结电容器。利用X射线衍射(XRD)、铁电测试仪等手段研究了保持温度对BFO薄膜结构和性能的影响。XRD图谱表明制备的BFO薄膜均为多晶结构,在保持温度400℃±2℃的区间内得到的BFO薄膜不含明显杂相,其它的温度均有明显的杂相。在保持温度为400℃时得到了较为饱和的电滞回线,在900 nm厚度的情况下,剩余极化强度仍可以达到Pr>40μC/cm2,达到了实际应用的要求Pr>10μC/cm2。漏电流拟合机制表明在低场下属于欧姆机制,在高场下比较接近空间电荷限制电流(SCLC)机制。     

紫光对外延掺锰铁酸铋薄膜物性的影响

采用溶胶-凝胶的方法在(001)取向的SrRuO3/SrTiO3 (SRO/STO)异质结上制备了外延BiFen95 Mn0.05O3(BFMO)薄膜,并以氧化铟锡(ITO)作为上电极构架了ITO/BFMO/SRO型电容器.研究表明,BFMO薄膜为良好的外延生长,当波长为404 nm的紫光入射到电容器表面,产生光电导,漏电流密度变大;测试电压为5V时,无光和光照时的漏电流密度分别为2.92 mA/cm2和10.10 mA/cm2.通过对电流密度的拟合发现:欧姆传导为外延ITO/BFMO/SRO电容器的主要漏电机制,并且光照没有改变电容器的导电机制.在紫光照射下,外延ITO/BFMO/SRO电容器的电滞回线发生变化,这是由于光照在薄膜内部产生光生载流子的缘故.由于光辐射的作用,外延ITO/BFMO/SRO电容器的电容增大.     

钙钛矿型氧化物电极对Ba0.6Sr0.4TiO3薄膜电学性能的影响

采用脉冲激光沉积技术(PLD)在单晶基片LaAlO3(001)、MgO(002)上分别制备Ba06Sr04TiO3/La0.5Sr05CoO3(BST/LSCO)、Ba0.6Sr04TiO3/SrRuO3 (BST/SRO)异质结构,研究了LSCO和SRO底电极对BST薄膜晶相结构、表面形貌及BST薄膜电容器的电学特性的影响.研究发现,沉积在钙钛矿氧化物底电极上的BST薄膜表面平整,并都具有良好的外延生长.由于生长在LSCO底电极BST薄膜的压应力大于生长在SRO底电极的压应力,BST/LSCO异质结构的介电可调率为79.58;,而BST/SRO的介电可调率仅为68.26;,两种底电极上生长的BST薄膜都具有较低的漏电流.     

溶胶-凝胶法制备BiFeO3薄膜的结构及物性研究

应用溶胶-凝胶法在Pt/Ti/SiO2/Si(001)基片上制备了BiFeO3薄膜,构架了Pt/BiFeO3/Pt电容器.采用X射线衍射仪和铁电测试仪研究了Pt/BiFeO3/Pt电容器的结构和物理性能.实验发现BiFeO3最佳的结晶温度为600 ℃,X射线衍射图谱显示BiFeO3薄膜结晶状况良好,原子力显微镜照片显示BiFeO3表面颗粒均匀.Pt/BiFeO3/Pt电容器具有良好的电学性能,在驱动电压为5 V的情况下,Pt/BiFeO3/Pt电容器的电滞回线具有良好的对称性,漏电流密度小于10-4 A/cm2,研究发现BiFeO3薄膜log(J)/log(E)关系满足空间电荷限制电流传导机制.     

外延生长四方相Pb(Zr0.65Ti0.35)O3薄膜

以SrRuO3(SRO)为缓冲层和底电极,利用射频溅射法在LaAlO3(LAO)单晶基片上制备了Pb(zr0.65Ti0.35)O3(PZT)薄膜.X射线衍射分析显示PZT薄膜与基底有以下外延取向关系:(001)[010]PZTⅡ(001)[010]SROⅡ(001)[010]LAO.虽然PZT薄膜组分位于菱方相区域,但由于基底的夹持效应,透射电子显微镜观察表明PZT薄膜呈现四方相.对以Pt或SRO为上电极的PZT薄膜的电性能分别进行了研究,结果显示两种样品都具有抗疲劳性,并且Pt/PZT/SRO薄膜电容与SRO/PZT/SRO薄膜电容相比具有更大的漏电流.氧化物基片和底电极的引入使得PZT薄膜的居里点与块材相比有所下降.电容-温度测试曲线表现出典型的居里-外斯定律特征,薄膜损耗随着温度上升而下降.当温度接近PZT薄膜相转变点的时候,由于夹持应力的解除导致薄膜损耗急剧下降.     

(001)高度择优取向Ba0.6Sr0.4TiO3/Pt异质结的结构及性能

采用射频磁控溅射法结合高真空后退火处理,在MgO(001)单晶基片上制备了Pt薄膜.应用脉冲激光沉积法在Pt/MgO上进一步生长了Ba0.6Sr0.4TiO3(BST)薄膜.借助X射线衍射仪(XRD)、铁电测试仪、LCR表研究了BST/Pt/MgO的结构和性能.研究发现,700 ℃真空退火可以保证Pt薄膜在MgO基片上实现(001)高度择优生长,以(001)Pt薄膜为模板,可以进一步获得(001)高度择优取向具有铁电性能BST薄膜.在100 Hz测试频率下,BST薄膜最大介电常数为1100、调谐率为81;、品质因数为21;在7 V的电压下,漏电流密度1.85×10-5 A/cm2,进一步分析表明,BST薄膜在0～2.6 V之间满足欧姆导电机制,在2.6～7 V之间满足普尔-弗兰克导电机制.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.