Defect microstructures in epitaxial PbZr0.2Ti0.8O3 films grown on (001) SrTiO3 by pulsed laser deposition

Transmission electron microscopy has been used to investigate the character and distribution of the microstructural features in epitaxial (001) ferroelectric PbZr_0.2Ti_0.8O₃ films grown on (001) SrTiO₃ substrates by pulsed laser deposition. The TEM observations revealed that the films were predominantly c-oriented with embedded a ₁- and a ₂-oriented domains lying on {101} planes. The substrate/film interfaces contained arrays of edge-type misfit dislocations and there were extraordinarily high densities ( ) of threading dislocations in the films. The character and distribution of these features are consistent with the following relaxation sequence. Firstly, the lattice misfit between the phases is accommodated at the growth temperature by the introduction of misfit dislocations at the edges of island nuclei, and some of these dislocations are forced away from the interface to form threading segments upon island coalescence. Next, the film adopts the c-orientation upon cooling through the Curie temperature with a ₁- and a ₂-oriented domains being formed to ameliorate the self-strain of the transformation. Finally, some redistribution of the embedded domains and misfit dislocations occurs in response to stresses caused by expansion coefficient differences. The impact of these defects on the electrical and electromechanical properties of epitaxial ferroelectric properties is discussed.     

Fabrication of 3-dimensional PbZr(1-x)Ti(x)O3 nanoscale thin film capacitors for high density ferroelectric random access memory devices

PbZr(x)Ti(1-x)O3 (PZT) thin films were deposited on 3-dimensional (3D) nano-scale trench structures for use in giga-bit density ferroelectric random access memories. PZT thin films were deposited by liquid delivery metalorganic chemical vapor deposition using Pb(thd)2, Zr(MMP)4, and Ti(MMP)4 precursors dissolved in ethyl cyclohexane. Iridium thin films were deposited by atomic layer deposition, and they exhibited excellent properties for capacitor electrodes even at a thickness of 20 nm. The trench capacitor was composed of three layers, viz. Ir/PZT/lr (20/60/20 nm), and had a diameter of 250 nm and a height of 400 nm. Almost 100% step coverage was obtained at a deposition temperature of 530 degrees C. The PZT thin film capacitors with a thickness of 60 nm on a planar structure exhibited a remnant polarization (Pr) of 28 microC/cm2, but the Pr value of the 3D PZT capacitors decreased slightly with decreasing 3D trench pattern size. The transmission electron microscope analysis indicated that the PZT thin films had compositional uniformity in the 3D trench region. Both columnar and granular grains were formed on the sidewalls of the trench capacitors, and their relative proportion exhibited strong size dependence. The trench capacitors with more columnar PZT grains showed good switching behavior under an external bias of 2.1 V and had a remnant polarization of 19-24 microC/cm2.     

Machine Detection of Enhanced Electromechanical Energy Conversion in PbZr0.2Ti0.8O3 Thin Films

Many energy conversion, sensing, and microelectronic applications based on ferroic materials are determined by the domain structure evolution under applied stimuli. New hyperspectral, multidimensional spectroscopic techniques now probe dynamic responses at relevant length and time scales to provide an understanding of how these nanoscale domain structures impact macroscopic properties. Such approaches, however, remain limited in use because of the difficulties that exist in extracting and visualizing scientific insights from these complex datasets. Using multidimensional band‐excitation scanning probe spectroscopy and adapting tools from both computer vision and machine learning, an automated workflow is developed to featurize, detect, and classify signatures of ferroelectric/ferroelastic switching processes in complex ferroelectric domain structures. This approach enables the identification and nanoscale visualization of varied modes of response and a pathway to statistically meaningful quantification of the differences between those modes. Among other things, the importance of domain geometry is spatially visualized for enhancing nanoscale electromechanical energy conversion.     

Investigation of PbZr0.4Ti0.6O3 capacitors with room temperature as-grown LaNiO3 electrodes

LaNiO₃ (LNO) film grown at room temperature (RT) by RF magnetron sputtering is used as the electrode for integrating LaNiO₃/PbZr_0.4Ti_0.6O₃/LaNiO₃ (LNO/PZT/LNO) capacitor on SrTiO₃ (STO) substrate. For comparison, LNO film grown at 250 °C is also used as the electrode of PZT capacitor. Reflection high energy electron diffraction (RHEED) technique is used to characterize the LNO film, it is found that LNO film prepared at 250 °C is epitaxial although no diffraction pattern is found for RT as-grown LNO. Ferroelectric properties of PZT films strongly depend on the LNO bottom electrodes. The remanent polarization (P _r) and coercive voltage (V _c), measured at 5 V, for the capacitors with LNO bottom electrodes prepared at RT and 250 °C, are 20 and 37 μC/cm², 1.67 and 1.95 V, respectively. No obvious degradation of polarization for PZT capacitors with RT as-grown LNO electrodes can be found. Room temperature as-grown LNO as both bottom and top electrodes to fabricate ferroelectric capacitors can save 2/3 thermal budgets, which may pay a way to decrease the potential challenges of devices resulting from the oxidation, interdiffusion or reactions during integrating ferroelectric capacitors with Si technologies.     

RF magnetron sputtering ferroelectric PbZr0.52Ti0.48O3 thin films with (001) preferred orientation on colossal magneto-resistive layers

Deposition by RF magnetron sputtering of PbZr_0.52Ti_0.48O₃ (PZT) ferroelectric thin films on two types of colossal magneto-resistive (CMR) oxide electrodes, La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO), is demonstrated in this work. The multiferroic heterostructure is grown on a STO substrate, which causes a 〈001〉 preferred orientation to develop. Ferroelectric, retention of polarisation and local piezoelectric properties were measured for assessing the success of the integration from the ferroelectric point of view. Remnant polarisation P_r and coercive field E_c were found to be ∼ 40 μC/cm² and ∼ 100 kV/cm, respectively. Films presented good retention of polarisation and piezoresponse loops. These results show that ferroelectric layers with good functionality can be grown on CMR oxide films, and open the possibility of designing a piezoelectrically driven spin valve memory cell device based on this heterostructure.     

强电场下PbZr0.4Ti0.6O3薄膜的电热效应

从Landau-Devonshire唯象理论出发,通过热力学分析得到了PbZr0.4Ti0.6O3体材料和薄膜的电热效应与温度和电场的关系.结果表明,在居里温度附近,体材料发生铁电相变,而在足够强的电场下,其固有的电热效应破坏了铁电相变的不连续性,绝热温度改变了约11K,对薄膜结构的PbZr0.4Ti0.6O3,绝热温度改变了约7.3K,这与实验结果(12K)基本相符.薄膜结构使铁电材料由不连续相变转到连续相变,它还减小了铁电材料的电热效应,降低了各物理量随温度变化的灵敏性.     

Low temperature sintering of Li1.1Nb0.58Ti0.5O3-xBi2O3 dielectric with adjustable temperature coefficient

Ceramics of Li_1.1Nb_0.58Ti_0.5O₃-xBi₂O₃ with low sintering temperature have been prepared by the solid-solution reaction method using B₂O₃ (2 wt% added) as sintering aid. For all compounds, the sintering temperature achieves 900 °C. Microstructure and dielectric properties of Li_1.1Nb_0.58Ti_0.5O₃-2 wt% B₂O₃-xBi₂O₃ (LNT-B-xBi) ceramics have been investigated. The X-ray diffraction patterns indicate for higher Bi₂O₃ content (x = 0.1 mol%) that the material is composed by two phases identified as M-phase and Bi₄Ti₃O₁₂. The Li_1.1Nb_0.58Ti_0.5O₃ + 0.15 mol% Bi₂O₃ composition sintered at 900 °C with B₂O₃ addition exhibits attractive dielectric properties (ε _r = 59.68, tan δ = 1.2×10^?4 and a temperature coefficient of the relative permittivity near zero) at 1 MHz. It is also shown that the introduction of Bi₂O₃ can tune the temperature coefficient of the relative permittivity. All dielectric properties lead this system compatible to manufacture sliver based electrodes multilayer dielectric devices.     

Synthesis of PbZr0.7Ti0.3O3 nanoparticles in a new tetragonal crystal structure with a polymer precursor

Nanoparticles (16- to 25-nm diameter) of PbZr_0.7Ti_0.3O₃, lead zirconate titanate (PZT), are synthesized by a controlled reconstructive thermal decomposition and crystallization from an amorphous polymer precursor with polyvinyl alcohol (PVA) and sucrose at 400 to 700 °C in air. When adding through a mixed acidic solution (with stirring) the ingredients of Pb²⁺ (nitrate) and Zr⁴⁺/Ti⁴⁺ (oxyhydroxides) cations mix-up with PVA-sucrose polymer molecules (dissolved in water) and reorganize in a dispersed structure of precursor. A dispersed structure of the cations through the polymer molecules retain on evaporating (at 50 to 80 °C in air) the excess water in a solid polymer precursor. It is found that a single phase compound of PbZr_0.7Ti_0.3O₃ forms on heating it at 400 to 700 °C temperature in air. It has a new tetragonal crystal structure in comparison to the rhombohedral bulk structure in the Zr-rich or the tetragonal structure in the Ti-rich PZTs. The PbZr_0.7Ti_0.3O₃ nanoparticles calcined under selected conditions in this polymorph are characterized by X-ray diffraction and microstructure in correlation with thermal analysis of the polymer precursor.     

锰掺杂对PbZr0.5Ti0.5O3铁电薄膜电学性能的影响

采用Sol-gel方法在生长有LNO3的Si(100)衬底上制备了掺Mn的PbZr0.5Ti0.5O3铁电薄膜(PMZT)。PMZT薄膜具有优良的铁电性。在外加电场下观察到了非对称剩余极化翻转行为。这种剩余极化的翻转不对称随着锰掺杂浓度的增加而变大,从而表明极化过程中产生的内建偏压电场是由Mn的掺杂引起的。当薄膜厚度保持不变时候,PMZT薄膜的剩余极化(Pr)和平均矫顽电场(Ec)随着锰掺杂浓度的增大而减小。在低频下,PMZT薄膜的介电常数随着锰的掺杂浓度的增加而减小。瞬时电流随着时间的呈指数衰减,最后到达饱和的稳态值。样品的漏电流密度随着电压的增加而近似地线性增加,显示出欧姆特性。在相同电压下,漏电流密度随着Mn掺杂浓度的增加而增加。     

Resistive-switching behavior in polycrystalline CaCu(3)Ti(4)O(12) nanorods

Highly aligned CaCu(3)Ti(4)O(12) nanorod arrays were grown on Si/SiO(2)/Ti/Pt substrates by radio-frequency sputtering at a low deposition temperature of 300 °C and room temperature. Structural and morphological studies have shown that the nanostructures have a polycrystalline nature and are oriented perpendicular to the substrate. The high density of grain boundaries in the nanorods is responsible for the nonlinear current behavior observed in these arrays. The current-voltage (I-V) characteristics observed in nanorods were attributed to the resistive memory phenomenon. The electrical resistance of microcapacitors composed of CaCu(3)Ti(4)O(12) nanorods could be reversibly switched between two stable resistance states by varying the applied electric field. In order to explain this switching mechanism, a model based on the increase/decrease of electrical conduction controlled by grain boundary polarization has been proposed.     

First observation of the reversible O3 ↔ P2 phase transition: Crystal structure of the quenched high-temperature phase Na0.74Ni0.58Sb0.42O2

According to thermal expansion data, O3-type phase Na_xNi_(1+x)/3Sb_(2−x)/3O₂ (x ≈ 0.8) undergoes at ca. 1270 K a reversible transition to a less dense form. The high-temperature phase quenched to liquid nitrogen belongs to P2 type, space group P6₃/mmc (no. 194), a = 3.0123 Å(2), c = 11.2264 Å(7) for x ≈ 0.74 at 298 K. The stabilisation of P2 versus O3-type structure at high temperatures seems to be due to alkali distribution over greater number of sites thus increasing entropy and decreasing Na⁺–Na⁺ repulsion.     

草酸-硝酸盐低热固相反应法制备(Ni_(0.58)Cu_(0.2)Zn_(0.22))Fe_(1.96)O_4铁氧体

以草酸和金属硝酸盐为原料,用低热固相反应法合成了纳米(Ni0.58Cu0.2Zn0.22)Fe1.96O4尖晶石型铁氧体,借助FT-IR、DSC-TG、XRD、TEM以及SEM等技术对固相反应过程和样品进行了研究及表征.FT-IR研究表明,草酸和金属硝酸盐在研磨过程中发生低热固相反应,生成金属草酸盐前驱体;FT-IR和XRD分析表明,前驱体经不同温度焙烧后得到单一尖晶石相的NiCuZn铁氧体粉末;依据TEM和SEM表征证明,前驱体在450℃分解1h后铁氧体粒径约为30～40nm,铁氧体于900℃烧结为陶瓷体后,晶粒约为2～4μml,烧结致密,磁谱测量表明,900℃烧结样品的磁导率为210,截止频率为28MHz.     

无铅Ba(Ce,Ti)O_3陶瓷的电卡效应

本文使用标准固相烧结法制备了Ba(Ti_(1-x)Ce_x)O_3(x=0.10,0.15,0.20)陶瓷,通过XRD分析发现这些陶瓷中除了Ba(Ti_(1-x)Ce_x)O_3主相外,还存在少量的杂相。利用Rietveld拟合的方法,获得了Ba(Ti_(1-x)Ce_x)O_3主相中的Ce/Ti实际比例。介电温谱表明这些陶瓷均存在一个明显的介电峰,且随着x的增加,峰值温度下降,介电峰宽展宽。利用不同温度下的电滞迴线,给出了不同温度和电场强度下的极化值,通过间接法获得了这些陶瓷的电卡效应。结果表明,BaTi_(0.9)Ce_(0.1)O_3的电卡效应最强,其DT值在403K和40kV/cm的电场下达到最大值,为0.48K,电卡强度为0.12×10~(-6)K·m/V。     

Flash-lamp-excited self-injection-seeded Q-switched Ti:Al(2)O(3) laser oscillator

A self-injection-seeded, flash-lamp-excited, Q-switched laser oscillator is presented. The laser comprises two resonators that are operated sequentially. The first resonator, which includes all the high insertion loss, damage prone, wavelength tuning, and line-narrowing components, is used to generate the seed signal. The second resonator is a low-loss, Q-switched resonator whose output wavelength and line width are controlled by the seed signal. Output pulses of energy as high as 325 mJ have been obtained that are tunable over a range of the order of 90 nm and with a bandwidth of the order of 0.05 nm.     

Position-controlled functional oxide lateral heterostructures consisting of artificially aligned (Fe,Zn)(3)O(4) nanodots and BiFeO(3) matrix

We demonstrate an advanced fabrication method for perfectly position-controlled ferromagnetic semiconductor (Fe,Zn)(3)O(4) nanodot arrays down to several hundred nanometers in size surrounded by a ferroelectric BiFeO(3) matrix. By performing position-selective crystal growth of perovskite BiFeO(3) on the position-controlled epitaxial spinel (Fe,Zn)(3)O(4) nanodot-seeding template, which is prepared using a hollow molybdenum mask lift-off nanoimprint lithography process on a perovskite La-doped SrTiO(3)(001) substrate, we produce functional oxide three-dimensional lateral heterojunctions. The position-selectivity can be explained based on standard surface diffusion theory with a critical nucleation point. Establishing this fabrication process could lead to innovative nanointegration techniques for spintronic oxide materials.