共查询到20条相似文献,搜索用时 15 毫秒
1.
S. H. Shah P. D. Bristowe A. M. Kolpak A. M. Rappe 《Journal of Materials Science》2008,43(11):3750-3760
The geometrical, chemical and ferroelectric properties of a new nanoscale short-period three-component SrTiO3/BaTiO3/PbTiO3 perovskite superlattice are investigated using a first principles density functional approach. The study focuses on varying
the thickness of each component in the superlattice and determining the resulting lattice distortion and total polarization.
Thicknesses of up to three unit cells in a single component are considered and the in-plane lattice constants normal to the
[001] stacking direction are fixed to the bulk SrTiO3 values to simulate a rigid substrate. It is found that the PbTiO3 layers play a key role in strain and polarization enhancement. By increasing the amount of PbTiO3 in the superlattices the strain in the other components increases significantly resulting in an enhanced total polarization
of the superlattice relative to bulk BaTiO3. Increasing the number of BaTiO3 layers also improves the overall polarization. All the SrTiO3 layers in each superlattice are found to be highly polarized. Many of the calculated features are similar to those found
previously by others for the SrTiO3/BaTiO3/CaTiO3 superlattice, although in the present study significantly greater enhancement factors and polarization values are found.
The predicted enhancement of the polarization is mostly attributed to lattice strain due to mismatch of the in-plane lattice
constant of the three-component materials. 相似文献
2.
Strontium titanate and barium titanate ceramics prepared by a reaction-sintering process were investigated. The mixture of
raw materials of stoichiometric SrTiO3 and BaTiO3 was pressed and sintered into ceramics without any calcination stage involved. A density 4.99 g/cm3 (97.5% of the theoretic value) was found in SrTiO3 after 6 h sintering at 1,370 °C. Grains less than 1.5 μm were formed at 1,300–1,330 °C and became 2.2–3.3 μm at 1,350–1,370 °C
SrTiO3. A density 5.89 g/cm3 (97.9% of the theoretic value) was found in BaTiO3 after 6 h sintering at 1,400 °C. Merged grains were observed in BaTiO3 and were less than 10 μm after sintered at 1,400 °C. 相似文献
3.
Multilayered oxide heteroepitaxial systems, including that of a 1-nm-thick Y2O3-stabilised ZrO2 (YSZ) sandwiched between layers of SrTiO3 (STO) [1], have been a subject of much interest lately due to their significantly enhanced ionic conductivities as compared to the
bulk materials. We aim to provide the foundation for understanding this increase in conductivity by considering the atomic
configurations at the interfaces of such systems, specifically a ZrO2/STO multilayer system. Possible stable lattice structures of pure ZrO2 in the system are explored using a genetic algorithm in which the interatomic interactions are modelled by simple pair potentials.
The energies of several of the more stable of these structures are then evaluated more accurately within density functional
theory (DFT). We find that the fluorite ZrO2 phase is unstable as a coherently strained epitaxial layer in the multilayer system. Instead, anatase-, columbite-, rutile-,
and pyrite-like ZrO2 epitaxies are found to be more stable, with the anatase-like epitaxy being the most stable structure over a wide range of
chemical potential of the components. We also find a high energy metastable structure resembling the tetragonal fluorite structure
which is predicted by DFT to be stabilised by SrO-terminated STO but not by TiO2-terminated STO. 相似文献
4.
5.
Xiaozan Guo Yugong Wu Yanan Zou Zhiyuan Wang 《Journal of Materials Science: Materials in Electronics》2012,23(5):1072-1076
Samples of xBiFeO3–(1 − x)BaTiO3 (x = 0, 0.02, 0.04, 0.06, 0.07 and 0.08) were synthesized by solid state reaction technique and sintered in air in the temperature
range 1,220–1,280 °C for 4 h. X-ray diffraction data showed that 2–8 mol% BiFeO3 can dissolve into the lattice of BaTiO3 and form single perovskite phase. The crystal structure changes from tetragonal to cubic phase at room temperature when 8 mol%
of BiFeO3 was added into BaTiO3. Scanning electron microscope images indicated that the ceramics have compact and uniform microstructures, and the grain
size of the ceramics decreases with the increase of BiFeO3 content. Dielectric constants were measured as functions of temperatures (25–200 °C). With rising addition of BiFeO3, the Curie temperature decreases. For the sample with x = 0.08, the phase transition occurred below room temperature. The boundary between tetragonal and cubic phase of the BiFeO3–BaTiO3 system at room temperature locates at a composition between 7 and 8 mol% of BiFeO3. The diffusivity parameter γ for compositions x = 0.02 and x = 0.07 is 1.21 and 1.29, respectively. The relaxor-like behaviour is enhanced by the BiFeO3 addition. 相似文献
6.
Wenjie Bian Xiaochi Lu Yaoyao Li Chengfa Min Haikui Zhu Zhenxiao Fu Qitu Zhang 《Journal of Materials Science: Materials in Electronics》2018,29(4):2743-2747
Sr1?x Nd x TiO3 (x?=?0.08–0.14) ceramics were prepared by conventional solid-state methods. The analysis of crystal structure suggested Sr1?x Nd x TiO3 ceramics appeared to form tetragonal perovskite structure. The relationship between charge compensation mechanism, microstructure feature and microwave dielectric properties were investigated. Trivalent Nd3+ substituting Sr2+ could effectively decrease oxygen vacancies. This reduction and relative density were critical to improve Q?×?f values of Sr1?x Nd x TiO3 ceramics. For ε r values, incorporation of Nd could restrain the rattling of Ti4+ cations and led to the reduction of dielectric constant. The τ f values were strongly influenced by tilting of oxygen octahedral. The τ f values decreased from 883 to 650 ppm/°C with x increasing from 0.08 to 0.14. A better microwave dielectric property was achieved for composition Sr0.92Nd0.08TiO3 at 1460 °C: ε r ?=?160, Q?×?f?=?6602 GHz, τ f ?=?883 ppm/°C. 相似文献
7.
E. P. Smirnova G. Yu. Sotnikova N. V. Zaitseva A. A. Kapralov G. A. Gavrilov 《Technical Physics Letters》2018,44(1):60-62
We have studied the electrocaloric effect in 0.68BaTiO3–0.32SrTiO3 solid solution, as well as the dielectric, pyroelectric, and piezoelectric properties of this compound in the vicinity of the first-order phase transition in a bias electric field. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed. 相似文献
8.
Microstructure, phase transition and electrical properties of (1 − x)K0.49Na0.51NbO3 − xLiSbO3 (x = 0–0.08) lead-free piezoceramics prepared by the conventional solid-state sintering method were investigated with an emphasis
on the effects of LiSbO3 doping amount x. SEM results showed that the ceramic became denser by increasing LiSbO3 doping amount x. Being indexed by XRD profiles, the ceramics changed from an orthorhombic perovskite structure to a tetragonal one across
a composition region of 0.04 ≤ x≤0.05. The sample of LiSbO3 doping amount x = 0.05 in tetragonal side of the region had the maximum values of piezoelectric constant (d
33 = 256 pC/N) and planar electromechanical coupling coefficient (k
p = 42.7%). Meanwhile, this ceramic sample showed other good properties such as ε
r = 1,463, tgδ = 0.036, Q
m = 48, P
r = 19.8 μC/cm2, E
c = 1.9 kV/mm and T
c = 340 °C, which indicated it was a promising lead-free piezoelectric material for ultrasonic transducer applications. 相似文献
9.
Perovskite type (Ba0.85Ca0.15?2x Bi2x )(Zr0.1Ti0.9?x Cu x )O3 lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 at room temperature. With the introduction of Bi2O3/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba0.85Ca0.15?2x Bi2x )(Zr0.1Ti0.9?x Cu x )O3 ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies. 相似文献
10.
Lead-free ferroelectric ceramics of (1−x) [0.88Na0.5Bi0.5TiO3-0.12K0.5Bi0.5TiO3]-x KNbO3(x = 0, 0.02, 0.04, and 0.06) were prepared by the conventional ceramic fabrication technique. The crystal structure, dielectric properties and P-E hysteresis loops were investigated. XRD data showed that all compositions could form pure perovskite structure. Temperature dependence of dielectric constant ε r and dissipation factor tanδ measurement between room temperature and 500∘C revealed that the compounds experience phase transitions that from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric in the range of x = 0–0.04. The frequency dependent dielectric constant showed these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant and dissipation factor increased sharply attributed to the superparaelectric clusters after the KNbO3 doped. 相似文献
11.
Mahamoud S. Alkathy K. C. James Raju 《Journal of Materials Science: Materials in Electronics》2016,27(9):8957-8965
Polycrystalline Sr(1–x)(Bi, Li)xTiO3 ceramics (x = 0 and 0.02) are prepared by a microwave processing method. The effect of co-substitution on structural, dielectric properties and ac-conductivity were investigated. The XRD of ceramics shows single phase with cubic structure. The lattice parameter of the compounds is estimated from the XRD patterns which confirm the incorporation of Bi and Li in SrTiO3 ceramics. Studies revealed that the dielectric constant and dielectric loss increased with an increase of temperature and decreased with an increase in frequency. The maximum dielectric constant obtained at room temperature is around 570 and increased to around 104 at 600 °C measured at 1 kHz frequency whereas the maximum dielectric loss measured was 0.048 at 600 °C and the loss measured at room temperature is 0.02. The activation energy of the samples were investigated using Arrhenius plots. 相似文献
12.
R. Moubah S. Colis G. Versini S. Barre C. Ulhaq-Bouillet A. Dinia 《Journal of Superconductivity and Novel Magnetism》2017,30(5):1171-1175
We report on the growth and magnetic properties of La2/3Sr1/3MnO3/SrTiO3/CoFe2 hard-soft magnetic systems prepared by pulsed laser deposition on SrTiO3(001) substrates. In situ reflection high-energy electron diffraction along the [100]SrTiO3 substrate azimuth and atomic force microscopy measurements reveal that La2/3Sr1/3MnO3 and SrTiO3 grow both in a three dimensional mode and that the roughness of the lower and upper magnetic/non-magnetic interfaces ranges between 2 and 4 Å. Cross-section transmission electron microscopy observations show that the layers are continuous, with an homogeneous thickness, and that the interfaces are mostly sharp and correlated. The magnetization curves show a two step reversal of the magnetization, with very distinct coercive fields. A small anisotropy is observed for the CoFe2 layer with an in plane easy magnetization axis along the [110]SrTiO3 direction. Minor magnetization loops indicate that the coupling between the magnetic layers is negligible. 相似文献
13.
Epitaxial trilayer heterostructures of the type La0.67Ca0.33MnO3/SrTiO3/La0.67Ca0.33MnO3 were grown by laser ablation on (001)[(LaAlO3)0.3+(Sr2AlTaO6)0.7] substrates. The real part of the dielectric permittivity ε and the loss factor tan δ of a 1100-nm-thick SrTiO3 interlayer were studied in the temperature interval T=4.2–300 K in a nonbiased state and at a bias voltage of ±2.5 V applied to the manganite electrodes. Using the temperature dependence ε(T) measured for the SrTiO3 layer grown between the manganite electrodes, we have estimated the capacitance of La0.67Ca0.33MnO3/SrTiO3 interfaces (C1≈2 μF/cm2) related to the electric field penetrating from the interlayer into La0.67Ca0.33MnO3. 相似文献
14.
15.
Y-modified Pb(SnTi)O3 polycrystalline materials with a general formula (Pb (Sn (PYST) (x = 0, 0.05, 0.07, 0.1) have been synthesized using the standard mixed oxide method. Crystallographic and surface morphology
studies are carried out by the powder X-ray diffraction and scanning electron microscopy techniques. X-ray diffraction studies
of the samples showed the tetragonal structure of the unit cell. Uniform grain distributions with porosity throughout the
surface of the sample pellets are observed. The T
C (transition temperature) increases with increase in the mole fraction of the substituent (x). ɛ/
max is found to decrease with increase in x. The slope of lnσac∼ 1/T shows distinct variations for temperature below 410 K, 410 K to T
c and for T > T
c. The room temperature ac conductivity at 10 kHz lies in the range of 10−5–10−6 (ohm−1 m−1). 相似文献
16.
V. N. Skrobot V. L. Ugolkov R. G. Grebenshchikov V. V. Gusarov 《Inorganic Materials》2007,43(12):1326-1329
The Tm2O3-Rh2O3 system has been studied by x-ray diffraction, thermal analysis, and chemical analysis of annealed and quenched samples. The results have been used to construct a schematic subsolidus phase diagram of the system. Only one double oxide, TmRhO3, has been identified. Some of its physicochemical properties are reported. 相似文献
17.
Feifei Wang Min Xu Tao Wang Yanxue Tang Wangzhou Shi 《Journal of Materials Science》2012,47(5):2352-2358
Phase transition and electrical properties were demonstrated for a Li-modified Bi0.5Na0.5TiO3-based solid solution. (0.935 − x)Bi0.5Na0.5TiO3 − xBi0.5Li0.5TiO3 − 0.065BaTiO3 with 0.5 mol% Mn doping was prepared by a conventional solid state reaction method. Close inspection of X-ray diffraction
patterns indicated that no characteristic peaks splitting happened, indicating the pseudocubic structure for all the compositions.
At a critical composition x of 0.06, optimized performance was obtained with piezoelectric constant d
33 of 176 pC/N, electromechanical coupling factors k
P of 0.33, and k
t of 0.52, respectively. In addition, it was found that the Li substitution could lead to a disruption of long-range ferroelectric
order and obtain enhanced frequency dispersion behavior accompanied with the decreasing of the depolarization temperature
T
d, which was responsible for the observed weaker ferroelectric polarization and electromechanical response. The composition
induced structure evolution was also discussed combined with the Raman spectroscopy. 相似文献
18.
Suhua Fan Fengqing Zhang Guitao Liu Qingbo Tian Luyi Zhu 《Journal of Materials Science: Materials in Electronics》2011,22(12):1778-1782
Bismuth-layered compound Ca0.15Sr1.85Bi4−xNdxTi5O18 (CSBNT, x = 0–0.25) ferroelectric ceramics samples were prepared by solid-state reaction method. The effects of Nd3+ doping on their ferroelectric and dielectric properties were investigated. The remnant polarization Pr of CSBNT ceramics
increases at beginning then decreases with increasing of Nd3+ doping level, and a maximum Pr value of 9.6 μC/cm2 at x = 0.05 was detected with a coercive field Ec = 80.2 kV/cm. Nd3+ dopant not only decreases the Curie temperature linearly, but also the dielectric constant (εr) and dielectric loss tangent (tan δ). The magnitudes of εr and tan δ at the frequency of 100 kHz are estimated to be 164 and 0.0083 at room temperature, respectively. 相似文献
19.
Winfried Mönch 《Journal of Materials Science: Materials in Electronics》2018,29(23):19607-19613
The intrinsic interface-induced gap states (IFIGS) which derive from the virtual gap states of the complex band structure are the fundamental mechanism that determines the band-structure lineup at semiconductor interfaces. The valence-band offsets of heterostructures are composed of a zero-charge-transfer term and an electrostatic-dipole contribution which are given by the difference of the p-type branch-point energies of the IFIGS and of the electronegativities, respectively, of the two semiconductors involved. The valence-band offsets of InGaZnO4, LaAlO3, and SrTiO3 heterostructures are quantitatively and consistently explained by the IFIGS-and-electronegativity concept. The analysis of the experimental InGaZnO4, LaAlO3, and SrTiO3 data yields the p-type branch-point energies as 2.37?±?0.18 eV, 2.59?±?0.13 eV, and 2.86?±?0.14 eV, respectively. 相似文献
20.
Xvqiong Li 《Journal of Materials Science: Materials in Electronics》2008,19(3):271-274
BaTiO3-based materials doped with SrBiO2.5 only show negative temperature coefficient effect over a wide temperature range. X-ray diffraction analysis displays that
major phases present in the sintered bodies were the Ba0.5Sr0.5TiO3 compounds with a cubic structure and the BaBiO3 compounds with a monoclinic structure. The mean grain size of samples remains unchanged with an increase from 20 to 50 in
SrBiO2.5 content. The values of ρ
25
and B
25/125
constants of thermistors decreased with an increase in SrBiO2.5 content. The resistivity measured at other temperatures showed basically the same behavior as that at room temperature, irrespective
of the measuring temperature. 相似文献