Microstructural evolution of [PbZr x Ti1– x O3/PbZr y Ti1– y O3] n epitaxial multilayers (x/y = 0.2/0.4, 0.4/0.6)–dependence on layer thickness

The microstructure of ferroelectric [PbZr _x Ti_{1? x} O₃/PbZr _y Ti_{1? y} O₃] _n epitaxial multilayers (x/y = 0.2/0.4, 0.4/0.6) deposited on SrRuO₃-coated SrTiO₃ substrates by pulsed-laser deposition with different layer periodicity and layer thickness was characterized by means of transmission electron microscopy. Electron diffraction and contrast analysis revealed a very clear and well-separated layer sequence. The microstructures of PbZr_0.2Ti_0.8O₃/PbZr_0.4Ti_0.6O₃ and PbZr_0.4Ti_0.6O₃/PbZr_0.6Ti_0.4O₃ multilayers show a similar tendency in the dependence on the individual layer thickness. Whereas with thick individual layers, tetragonal a-domains are confined to specific layers of the two types of multilayers, below a certain critical thickness of the individual layers, a-domains extend over the whole film. This indicates a transition into a uniform tetragonal lattice and strain state of the whole multilayer. Increasing the layer periodicity further, the interfaces in PbZr_0.4Ti_0.6O₃/PbZr_0.6Ti_0.4O₃ multilayers become rough, and complex a-domain configurations appear.     

The pyroelectric effect in magnetoelectric 0.8 PZT-0.2 MZF and 0.8 PZT-0.2 NZF composites

The pyroelectric response is measured using the dynamic method in preliminarily polarized magnetoelectric 0.8PbZr_0.53Ti_0.47O₃-0.2Mn_0.4Zn_0.6Fe₂O₄(0.8 PZT-0.2 MZF) and 0.8PbZr_0.53Ti_0.47O₃-Ni_0.4Zn_0.6Fe₂O₄ (0.8 PZT-0.2 NZF) composites, where PZT is a ferroelectric, and MZF and NZF are manganese-zinc and nickel-zinc ferrites, respectively. Values of the pyroelectric coefficient Γ for the materials under study vary over the range of 1.5–4 × 10⁻⁸ C cm⁻² K⁻¹. It is shown that the polarized samples of the composites have a heterogeneous distribution of polarization across the sample thickness. The heterogeneity is more pronounced in the near-surface layers of the investigated materials.     

锆钛酸铅双层膜的铁电及光学特性研究

采用化学溶液沉积法在LaNiO₃涂布的硅晶片上制备了高度(100)择优取向,表面均匀、平整、致密无裂纹的PbZr_0.5Ti_0.5O₃/PbZr_0.4Ti_0.6O₃双层膜. 双层膜具有单一的钙钛矿相,同时拥有良好的铁电性能,剩余极化强度高达64μC/cm²,平均矫顽场仅为43.6kV/cm. 棱镜-薄膜耦合实验结果表明PbZr_{关键词： 铁电薄膜 平板光波导 锆钛酸铅 棱镜-薄膜耦合}     

Atomic-force microscopy of polarization domains in ferroelectric films

Single-crystal (001)-oriented PbZr_0.47Ti_0.53O₃ and polycrystalline (111)-oriented PbZr_0.47Ti_0.53O₃ thin ferroelectric films were studied using contact electrostatic force microscopy. Local electromechanical response measurements permitted study of the polarization vector distribution in natural and intentionally created polarization nanodomains in films. The principal components of an electromechanical response signal encountered in studies of ferroelectric films (the piezoelectric response and the additional capacitive contribution) were isolated and analyzed. The effect of tip-surface contact stiffness on the capacitive contribution to the electromechanical response signal was demonstrated experimentally and in terms of a model. It was shown that more accurate information on the distribution of the polarization vector in ferroelectric films can be gained by monitoring local variations in the tip-surface contact stiffness.     

Temperature-electric field hysteresis loop of multicaloric effects in PbZr0.8Ti0.2O3 thin films

The Multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin films is investigated with the application of sine wave electric field, dc electric field and stress using a phase field method combined with the thermodynamic analysis. The simulation results show that the adiabatic temperature change-electric field curve presents a shape of butterfly in the presence of the sine wave electric field. In order to detect the effect of the sine wave electric field, the multicaloric effect and the domain structures under the direct electric field and the sine wave electric field are compared. It is found that the domain switching behaviors are quite different under the different applied electric fields. And the negative multicaloric effect in the PbZr_0.8Ti_0.2O₃ thin film is attribute to the domain switching under the external field.     

Control of the temperature hysteresis and diffuse dielectric anomaly in the temperature range of the ferroelectric-antiferroelectric phase transition in PbZr1 − x TixO3 (0.03 ≤ x ≤ 0.05) ceramics

The magnitudes of the temperature hysteresis and diffuse dielectric anomaly corresponding to the transition from the antiferroelectric phase to the ferroelectric phase in PbZr_{1 ? x} Ti_xO₃ (0.03 ≤ x ≤ 0.05) ceramics can be reversibly changed by varying the temperatures of heating and cooling in the course of thermocycling. The results obtained indicate that the antiferroelectric-ferroelectric transition in the PbZr_{1 ? x} Ti_xO₃ ceramics materials is a smeared first-order phase transition.     

Field-induced vortices in weakly anisotropic ferroelectrics

In microscale and nanoscale ferroelectric samples, the formation and growth of domains are the usual stages of the polarization switching mechanism. By assuming weak polarization anisotropy and by solving the Ginzburg–Landau–Khalatnikov equation we have explored an alternative mechanism which consists in ferroelectric switching induced by vortex formation. We have studied the polarization dynamics inside a ferroelectric circular capacitor where switching leads to the formation of a metastable vortex state with a rotational motion of the polarization. Our results are consistent with recent first-principle simulations [I.I. Naumov, H.X. Fu, Phys. Rev. Lett. 98, 077603 (2007)] and with experiments on PbZr_0.2Ti_0.8O₃ [A. Gruverman, D. Wu, H.J. Fan, I. Vrejoiu, M. Alexe, R.J. Harrison, J.F. Scott, J. Phys. Condens. Matter 20 342201(2008)] and demonstrate that vortex-induced polarization switching can be an effective mechanism for circular nanocapacitors.     

Infrared optical properties of PbZr0.4Ti0.6O3/La0.5Sr0.5CoO3 heterostructures on platinized silicon substrate

PbZr_0.4Ti_0.6O₃/La_0.5Sr_0.5CoO₃ heterostructures have been grown on Pt/Ti/SiO₂/Si substrates by chemical solution routes. Optical properties of the PbZr_0.4Ti_0.6O₃/La_0.5Sr_0.5CoO₃ heterostructures were studied by infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5–12.5 m. The optical constants of PbZr_0.4Ti_0.6O₃ and La_0.5Sr_0.5CoO₃ thin films were determined by fitting the IRSE data using a classical dielectric model and a Drude dielectric model, respectively. For PbZr_0.4Ti_0.6O₃ thin films, the refractive index decreases and the extinction coefficient increases as the wavelength increases. For La_0.5Sr_0.5CoO₃ thin films, the refractive index and the extinction coefficient increase as the wavelength increases. The absorption coefficient of La_0.5Sr_0.5CoO₃ thin films is greater than 10⁴ cm^-1 for the wavelength range of 2.5–12.5 m. The absorption coefficient of PbZr_0.4Ti_0.6O₃ thin films on a La_0.5Sr_0.5CoO₃/Pt/Ti/SiO₂/Si substrate is smaller than that on a Pt/Ti/SiO₂/Si substrate by a factor of two. PACS 77.84.Dy; 78.20.Ci; 81.20.Fw     

Ultrafast structural dynamics of perovskite superlattices

Femtosecond x-ray diffraction provides direct insight into the ultrafast reversible lattice dynamics of materials with a perovskite structure. Superlattice (SL) structures consisting of a sequence of nanometer-thick layer pairs allow for optically inducing a tailored stress profile that drives the lattice motions and for limiting the influence of strain propagation on the observed dynamics. We demonstrate this concept in a series of diffraction experiments with femtosecond time resolution, giving detailed information on the ultrafast lattice dynamics of ferroelectric and ferromagnetic superlattices. Anharmonically coupled lattice motions in a SrRuO₃/PbZr_0.2Ti_0.8O₃ (SRO/PZT) SL lead to a switch-off of the electric polarizations on a time scale of the order of 1 ps. Ultrafast magnetostriction of photoexcited SRO layers is demonstrated in a SRO/SrTiO₃ (STO) SL.     

氧压对SrTiO3和SrNb0.2Ti0.8O3薄膜晶格参数的影响及激光感生热电电压效应

采用脉冲激光沉积技术制备了SrTiO₃和SrNb_0.2Ti_0.8O₃薄膜.X射线衍射分析表明在LaAlO₃(100)单晶平衬底上生长的SrTiO₃及SrNb_0.2Ti_0.8O₃薄膜是沿［001］取向的近外延生长.随着氧压在一定范围内逐渐增大,SrTiO₃薄膜的晶格参数减小,而SrNb_0.2Ti_0.8O₃薄膜的晶格参数先减小后增大.同时摸索出制备具有二维电子气超晶格(SrTiO₃/SrNb_0.2Ti_0.8O₃)_L的最佳氧压为1.0×10^-2Pa.另外在LaAlO₃(100)倾斜衬底上制备的SrNb_0.2Ti_0.8O₃薄膜中观察到激光感生热电电压效应. 关键词： 0.2Ti_0.8O₃薄膜')" href="#">SrNb_0.2Ti_0.8O₃薄膜 晶格参数 激光感生热电电压 脉冲激光沉积     

Effect of internal strain fields on the controllability of nanodimensional ferroelectric films in a plane capacitor

Nanodimensional ferroelectric heteroepitaxial Ba_0.8Sr_0.2TiO₃ films grown by the layer-by-layer mechanism on MgO(100) substrates are examined by the X-ray diffraction and transmission electron microscopy methods. It is established that, when the thickness of the film changes, the stress relaxation proceeds via generation of misfit dislocations at the film-substrate interface. There exists a critical thickness (≈40 nm) of the film below and above which the film possesses tensile and compression stresses, respectively. Examples of how the stresses influence the insulating properties of the films are given.     

High-resolution transmission electron microscopy of heteroepitaxial barium strontium titanate films grown on MgO substrates

Nanoscale (5–100 nm) ferroelectric heteroepitaxial Ba_0.8Sr_0.2TiO₃ films on MgO(001) substrates were studied by methods of high-resolution transmission electron microscopy using Tecnai G² and FEI Titan 80–300 microscopes. Misfit dislocations resulting from stress relaxation in films and insignificant local misorientation of film regions (block structure) were detected. The heterostructure was numerically simulated, which allowed the detection of the formation of oxygen (substrate)-titanium (film) bonds or the oxygen (substrate)-barium (film) bond at the film-substrate interface.     

Phase transitions in xPbZr0.53Ti0.47O3-(1 − x)Mn0.4Zn0.6Fe2O4 magnetoelectric composites

The elastic, inelastic, and dielectric properties of the magnetoelectric composite xPbZr_0.53Ti_0.47O₃-(1 ? x)Mn_0.4Zn_0.6Fe₂O₄ (PZT-MZF) are studied in the temperature range from room temperature to 673 K. The influence of the ferroelectric PZT phase on the magnetic phase transition and the magnetic MZF phase on the ferroelectric phase transition is revealed. It is established that, as the PZT content increases, the degree of diffuseness of the phase transition decreases and a gradual crossover from a pronounced relaxor behavior to a more ordered ferroelectric behavior occurs.     

Pyroelectric and piezoelectric hysteresis loops in thin PZT films with excess lead oxide

Comparative analysis of pyroelectric and piezoelectric hysteresis loops of thin PbZr_0.54Ti_0.46O₃ + 10 mol % PbO films formed under the same conditions on pyroceram and silicon substrates has been performed. The significant differences in the behavior of the parameters under study are attributed to the different character of the biaxial stress acting on a ferroelectric film from pyroceram and silicon substrates.     

Contribution of structural order-disorder to the room-temperature photoluminescence of lead zirconate titanate powders

Intense and broad visible photoluminescent (PL) band was observed at room temperature in structurally disordered PbZr_0.53Ti_0.47O₃ powders. The lead zirconate titanate PbZr_0.53Ti_0.47O₃ powders prepared by the polymeric precursor method and heat treated at different temperatures were structurally characterized at long range by means of X-ray diffraction. The PL was measured at room temperature samples heat treated at different temperatures. Experimental measurements and quantum-mechanical calculations showed that the high structural order and the high structural disorder in PbZr_0.53Ti_0.47O₃ lattice are not favorable to the intense PL emission. Only samples containing simultaneous structural order and disorder in their lattice present the intense visible PL emission at room temperature.     

The Field Effect in a Metal–Ferroelectric–Semiconductor System of Multilayer Ferroelectric Films with Various Structure Types

The ability to grow the interfacial defect-poor Sr_0.5Ba_0.5Nb₂O₆ + Ba_0.2Sr_0.8TiO₃ and Ba_0.8Sr_0.2TiO₃ + Ba_0.4Sr_0.6TiO₃ ferroelectric films onto the doped silicon substrates is discussed. A study of piezo-response via the quasi-static method (using the electrode area of 0.07 mm²) reveals that heterostructures possess an initial polarized ferroelectric state with a spontaneous polarization vector perpendicular to the substrate at any type of Si conductivity. The polarized state is established to refer to two-dimension stresses in the ferroelectric, which is tunable through a preprepared Ba_xSr_{1 – x}TiO₃ onto a sublayer substrate as well as to a thickness of this sublayer. Polarization switching in Sr_0.5Ba_0.5Nb₂O₆/Si and Ba_0.8Sr_0.2TiO₃/Si heterostructures under the external field arises at only using the barium–strontium titanate sublayer predeposited onto silicon. A 15% decrease in switching polarization in Ba_0.8Sr_0.2TiO₃/Ba_0.4Sr_0.6TiO₃/Si structures is observed after 500 h.     

Pressure-enforced plasticity in MAX phases: from single grain to polycrystal investigation

Ti₄AlN₃, Ti₃AlC₂ and Ti₃Al_0.8Sn_0.2C₂ MAX phases were plastically deformed at room temperature (RT) under gaseous confining pressure. Microstructures of as-grown and deformed samples are carefully analysed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is demonstrated that high level of plastic deformation can be reached under confining gas pressure; the later suppresses the brittle failure at RT to the profit of plasticity. Multiscale characterization techniques are shown to provide a unique insight into all the scales of the plastic deformation; in particular, the effect of the mesoscale. Indeed, grain shape and orientation relative to the compression axis are shown to play a key role in the deformation process, intergranular stresses leading to a complex stress field in the polycrystalline samples. The TEM results show that dislocation activity highly depends on the grain orientation. The observation of dislocation entanglements unambiguously demonstrates that dislocations may be organized in such a configuration so that their glide in the basal plane can be hindered when deep plastic regime is reached.     

First-principles study on the geometric and electronic structures and phase transition of PbZr1-xTixO3 solid solutions

With first-principles virtual-crystal approximation calculations, we systematically investigate the geometric and elec- tronic structures as well as the phase transition of lead zirconate titanate (PbZr1-xTixO3 or PZT) as a function of Ti content for the whole range of 0 ≤ x Ti ≤ 1. It can be found that, with the increase of the Ti content, the PbZr1-xTixO3 solid solu- tions undergo a rhombohedral-to-tetragonal phase transition, which is consistent with the experimental results. In addition, we also show the evolution in geometric and electronic structures of rhombohedral and tetragonal PbZr1-x TixO3 with the increasing content of Ti.     

SEM,SAED, and TEM investigations of domain structure in PZT ceramics at morphotropic phase boundary

SEM investigations of ferroelectric domain structure in PbZr_0.53Ti_0.47O₃ are consistent with a model of spatial domain configuration for the piezoelectric ceramics previously proposed for BaTiO₃. TEM and SAED results revealed not only the twinning relation of adjacent tetragonal 90° domains but also the simultaneous presence of the ferroelectric rhombohedral phase. A succession model of ferroelectric domains T₁RT₂RT₁... which needs a smaller energy for the rotation of the polarization vector due to the coexistence of a R domain between the two T 90° domains is proposed. This model is also confirmed by the estimated value of elastically stored energy in the mixed wall and by the dependence upon the sintering temperature of T and R unit cell distortions previously measured by x-ray diffraction.     

Evolution from relaxor-like dielectric to ferroelectric in Ba[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ (x=0.2,0.4,0.6,0.8,0.85,0.9 and 0.95) solid solutions were synthesized by a standard solid-state reaction technique. X-ray diffraction at room temperature and dielectric characteristics over a broad temperature and frequency range were evaluated systematically. The structure of Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ solid solutions changed from cubic to tetragonal with increasing x. A Debye-like dielectric relaxation following the Arrhenius law similar to that in Ba(Fe_0.5Nb_0.5)O₃ was observed at lower temperature in the composition range 0.2≤x≤0.8, while the relaxor ferroelectric, diffused ferroelectric and normal ferroelectric behavior were observed for x=0.85,0.9 and 0.95, respectively. The process of the evolution of relaxor-like dielectric to ferroelectric suggested the changing from dilute polar micro-domains to polar micro-domains, polar micro/macro-domains and then polar macro-domains in the present ceramics.