Electrostrictive mechanism of microwave losses in a planar strontium titanate film capacitor

An analysis is made of the dielectric losses in the microwave range in a planar ferroelectric capacitor caused by electrostrictively excited sound in the ferroelectric in the presence of a bias field (induced piezoeffect). An approximate expression is obtained for the dielectric loss tangent as a function of the bias field and the frequency. Numerical estimates are made for singlecrystal strontium titanate at 78 K. This loss mechanism may be a determining factor for the fabrication of planar capacitors using high-quality ferroelectric films having properties close to those of the single crystal. Zh. Tekh. Fiz. 69, 93–99 (August 1999)     

Thermostable ferroelectric capacitors based on graded films of barium strontium titanate

Technical Physics - The influence of the pressure of working gas during the ion–plasma sputtering on properties of deposited ferroelectric barium strontium titanate coatings has been...     

Domain epitaxial growth of ferroelectric films of barium strontium titanate on sapphire

A model of the epitaxial growth of crystalline multicomponent films on single-crystal substrates with a domain correspondence is presented using a solid solution of barium strontium titanate on sapphire substrates (r cut). The domain epitaxial growth suggests the matching of the lattice planes of the film and the substrate having similar structures by comparison of domain multiple of an integral number of the interplanar spacings. Variation of the component composition of the solid solution enables changes in the domain size in the range sufficient for epitaxial growth. This method can be used to project the epitaxial growth of films of various solid solutions on single-crystal substrates.     

Raman spectra of a barium strontium titanate film in electric fields

Polarized Raman spectra of a heteroepitaxial barium strontium titanate film on a MgO substrate were studied in an external electric field applied perpendicular to the direction of spontaneous polarization. The partial depolarization observed in the spectra indicates the electric-field-induced reduction of the symmetry of the crystal lattice.     

Influence of the substrate temperature on the initial stages of growth of barium strontium titanate films on sapphire

The initial stages of growth of ferroelectric films of barium strontium titanate BaSrTiO₃ on singlecrystal sapphire substrates have been experimentally investigated as a function of the deposition temperature. It has been shown that, at the initial stage of the condensation of the BaSrTiO₃ film on sapphire, the temperature of the substrate determines the mechanisms of mass transfer of deposited atoms and the processes of nucleation.     

高温超导薄膜J_c与微波非线性相关性研究

采用微带谐振器技术研究高温超导薄膜的微波非线性问题,介绍了微波非线性的测试方法,描述了测试现象,定量表征了微波功率非线性。将微波非线性与临界电流密度Jc大小的关联性进行分析研究,发现两者关联性弱;同时验证了功率压缩测试方法对高温超导薄膜微波非线性的研究是可行的。     

Effect of zero-point energy on the dielectric behavior of strontium titanate

Barrett formula has been obtained in the framework of the effective field approach by including the zero-point energy. By fitting with experimental data of dielectric constant of SrTiO₃, we find that they agree in the whole temperature range fairly well if the zero-point energy is assumed to change from a small value at low temperature to a large value at high temperature.     

Physical states and properties of barium titanate films in a plane electric field

The influence of a plane electric field on the phase states of barium titanate thin films under the conditions of forced deformation has been studied. The field dependence of a complete set of material constants has been taken in the region of the c-phase, where polarization losses are absent. The material constants are calculated using equations of the piezoelectric effect derived by linearizing the nonlinear equations of state from the phenomenological; theory for barium titanate. It has been shown that there is a critical value of the field at which the electromechanical coupling coefficient reaches a maximum.     

Quasi-ordered nanostructures on the surface of strontium titanate

The results of the investigation of the surface of strontium titanate single crystals after treatment with high-energy plasma are presented. The surface morphology of the strontium titanate single crystals and the change in its characteristics after plasma treatment have been studied using electron scanning and atomicforce microscopy. A change in the electronic state of a part of the titanium ions and a change in the stoichiometry in the modified near-surface layer have been found by the method of valence shift of X-ray lines. A preliminary analysis has been made of the conditions providing the formation of single- and two-level systems of ordered crystallites with sizes of 10⁻⁷–10⁻¹⁰ m on the surface of single-crystal strontium titanate with impurities of ions of the iron and lanthanum groups.     

Effect of Mg doping on the structural and dielectric properties of strontium titanate ceramics

The influence of Mg incorporation into A- and B-sites of the perovskite lattice of SrTiO₃ ceramics on the structural, microstructural and low-frequency dielectric properties is studied in this work. Compounds in the systems Sr_1-xMg_xTiO₃ and SrTi_1-yMg_yO_3- were synthesised by a conventional solid-state method. The solid solubility of Mg is restricted to x<1% for A-site occupancy (Sr_1-xMg_xTiO₃) and to y<15% for B-site occupancy (SrTi_1-yMg_yO_3-). The lattice parameter is found to increase with Mg content for the SrTi_1-yMg_yO_3- system, while it is almost invariant in the Sr_1-xMg_xTiO₃ one. The dependence on the lattice-site occupancy is also verified for the grain growth of ceramics. For SrTi_1-yMg_yO_3- the average grain size markedly decreases with increasing Mg content. For Sr_1-xMg_xTiO₃ the inverse dependence is observed. Contrary to expectations, Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, located in either A- or B-sites of the SrTiO₃ lattice. Moreover, fitting the dielectric behaviour to Barretts law demonstrates that B-site doping drives the system away from the ferroelectric instability. In Mg-doped strontium titanate ceramics the dielectric permittivity and dielectric losses decrease. The results are discussed based on the correlation between cation-site occupancy, charge and chemical stoichiometry in both systems. PACS 61.10.Nz; 68.37.Hk; 68.37.Lp; 77.22.Ch; 77.22.Gm; 77.84.Dy     

Relaxation of electronic excitations in strontium titanate

The transient absorption spectra and kinetics were studied for undoped, lead doped and high purity SrTiO 3 single crystals. The pulsed electron beam induced transient absorption is studied in all crystals. The strong absorption at 0.8 v eV was observed only in high purity SrTiO 3 . This absorption is suggested to arise from intrinsic electron polaron. The bound electron polarons are likely responsible for absorption band at 1.4 v eV. The main luminescence band under excitation pulse is observed at 2.75 v eV. The luminescence decay is faster than that of transient absorption.     

Kinetics of oxygen exchange in strontium titanate

The kinetics of oxygen exchange are of primary importance for the application of titanates as fast resistive oxygen sensors. The sensor’s conductivity is correlated with the oxygen partial pressure pO₂ of the surrounding atmosphere: Due to oxygen surface transfer and subsequent diffusion of oxygen vacancies V _O ^·· , a pO₂ change gives rise to a conductivity change of the sample. While bulk diffusion usually occurs very fast, the surface transfer reaction becomes the rate determining step for thin samples and for low temperatures. We have shown that in the case of acceptor doped SrTiO₃ the kinetics of the surface transfer reaction can be strongly influenced through stoichiometric changes brought about by thin coatings of alkaline earth metal oxides (e.g. SrO). In contrast to the commonly used jump method (conductivity response to a sudden pO₂ change in the time domain), a model is presented which is based on the frequency-domain analysis of amplitude and phase shift of the response signal obtained from a pO₂ modulation in a fast kinetic measurement set-up. This method allows not only for measuring response times in the sub-millisecond range but also for distinguishing between behaviour either controlled by volume diffusion or by surface transfer reaction. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

Growth of epitaxial c ‐plane ZnO film on a ‐plane sapphire by radio frequency reactive magnetron sputtering

In this Letter, we report the successful growth of high quality c ‐plane oriented epitaxial ZnO films on a ‐plane sapphire substrates by using radio frequency reactive magnetron sputtering. The effect of substrate temperature on the structural and optical properties has been investigated. X‐ray diffraction (XRD) studies reveal that the ZnO film is grown epitaxially on a ‐plane sapphire substrate, and the film quality is improv‐ ed as the substrate temperature is increased. Photoluminescence (PL) results manifest that screw dislocations can exert great influence on the optical properties. It is found that the line width of the near‐band‐edge emission of PL decreases linearly with increase in screw density. In addition, a simple and effective method is proposed to assess the defect density in epitaxial ZnO films by performing PL measurement. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the magnetic field in the plane of a garnet ferrite film with orthorhombic magnetic anisotropy on the dynamics of domain walls

The effect of an in-plane magnetic field on the dependence of the domain-wall velocity on the acting magnetic field is investigated for bismuth-containing garnet ferrite single-crystal films of the composition (Bi,Y,Pr)₃(Fe,Ga)₅O₁₂ with the (210) orientation. The in-plane magnetic field is applied along the 〈120〉 and 〈001〉 crystallographic axes. The domain-wall velocity is measured in directions perpendicular and parallel to the in-plane magnetic field.     

ESR study of impurities in strontium titanate films

The paper reports on an ESR study of Cr-and Ca-codoped SrTiO₃ films, 1700 and 350 nm thick, before and after UV irradiation (λ=365 nm). The spectrum of the thick film (1700 nm) exhibits two ESR lines with g factors of 1.977 and 1.974, which belong to the Cr³⁺ centers. In the spectrum of the thin film (350 nm), one observes only one line, which is due to the chromium center with a g factor of 1.974. Calculations showed that the line with the smaller g factor belongs to the Cr³⁺ center located close to the film surface. The weak line observed in the spectrum after UV irradiation (g factor = 2.012) is most likely due to the O^? center. The regions of thermal stability of the observed centers were studied. A comparative analysis of the characteristics of impurities in bulk samples and films was carried out.     

Josephson effect in the strontium titanate/lanthanum aluminate junction

We report theoretical studies on the newly discovered novel Josephson effect and scanning tunneling spectroscopy(STS) at the interface of strontium titanate/lanthanum aluminate(STO/LAO).With a phenomenological boson–fermion model, the density of states is calculated and the results are consistent with the STS experiments.A typical calculation of Josephson effect is performed, and it is in qualitative agreement with the experiments.The calculations indicate that the gap states come from the pairing of quasi-particles with a finite total momentum and the Josephson current comes from the tunneling of quasi-particle pairs with zero momentum.The quasi-particles are Bogoliubov quasi-particles.Moreover, the fits using Kulik's formula imply that the Josephson junction at the STO/LAO interface has a point contact with the clean superconductor limit.     

金属纳米粒子薄膜对辐射散热的影响的研究

通过分析不同螺旋线慢波组件的散热性能,研究了金属纳米粒子薄膜的采用对辐射散热性能的改善作用.利用实验测试和模拟仿真的方法,分析比较了采用普通金属管壳,沉积普通金属铱膜管壳和沉积纳米铱膜管壳的慢波组件的导热能力.结合实验数据,准确地推算出几种研究材料的热辐射发射率,并利用模拟仿真给予了验证.实验结果和模拟结果具有很好的一致性.研究表明,与普通金属材料相比,金属纳米粒子薄膜具有较强的热辐射能力,能够改善器件的散热性能.     

Thermal tunability in terahertz metamaterials fabricated on strontium titanate single-crystal substrates

We report an experimental demonstration of thermal tuning of resonance frequency in a planar terahertz metamaterial consisting of a gold split-ring resonator array fabricated on a bulk single-crystal strontium titanate (SrTiO?) substrate. Cooling the metamaterial starting from 409 K down to 150 K causes about a 43% shift in resonance frequency, and there is very little variation in resonance strength. The resonance shift is due to the temperature-dependent dielectric constant of the strontium titanate. The experiment opens up avenues for designing tunable terahertz devices by exploiting the temperature-sensitive characteristic of high dielectric constant substrates and complex metal oxide materials.     

Effect of magnetic field on the thermal nonlinearity of surface waves in plasma-metal structures

A study is made into the effect of the nonlinear mechanism of plasma electron heating on the dispersion properties of potential surface waves propagating along the interface between a metal and finite-pressure magnetoactive plasma. An external steady magnetic field is directed normally to the interface. Different mechanisms of electron energy loss are treated in a weak heating approximation. The energy balance equation is used to determine the spatial distribution of the plasma electron temperature under conditions of nonlocal heating. The effect of the plasma parameters on the nonlinear shift of the wavenumber and on the spatial damping factor of surface waves is investigated. The results obtained are valid for both semiconductor and gaseous plasmas.