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1.
用全电势线性缀加平面波法(FLAPW)计算了KTa0.5Nb0.5O3四方相和立方相 的光学特性,即介电函数虚部ε2(ω)、光学吸收系数I(ω)和反射率R(ω). 在四方相,介电虚部沿a,b轴,在3,7和23eV附近,分别有三个介电峰.沿c轴的三个介电峰分别位于4,8和23eV.其中4eV附近的介电峰非常尖锐而且高.从8至18eV,沿a,b ,c轴三个方向都有许多低的介电峰.通过对两相光学特性的对比分析发现铁电相KTa0.5Nb0.5O3具有更强的各向异性.
关键词:
平面波法计算
光学常量和参数
铁电体 相似文献
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《Optics Communications》2002,201(1-3):79-84
Using density functional methods, optical properties of KTa0.5Nb0.5O3 (KTN) are investigated. The imaginary part of dielectric function ε2(ω), the optical absorption coefficient I(ω) and the reflectivity R(ω) of KTN in the cubic (paraelectric) and tetragonal (ferroelectric) phases are calculated. The origin of the different behavior of the optical spectra between the two phases is discussed. 相似文献
4.
Zheng Ke-yu Wei Nian Yang Feng-xia Zhang Duan-ming Qi Ya-jun 《Frontiers of Physics in China》2007,2(4):436-439
Potassium tantalate niobate (KTa0.4Nb0.6O3, KTN) nanoparticles of perovskite structure were successsfully synthesized by a solvothermal method. The KTN nanoparticles
synthesized at 250 °C for 8 h with 1 to 4 M KOH concentration using isopropyl alcohol [(CH3)2 CHOH] as the solvent was composed of a single phase of cubic perovskite structure. Futhermore, the KTN powers synthesized
at the same conditions besides of using (CH3)2CHOH/H2O as a solvent compose of a single phase of tetragonal perovskite structure. The nanoparticles exhibit a mixture of cubic
and prism-like shapes with lengths of 100 nm to 500 nm and average cross sections of 200×200 nm2. The solvent dependence of the powder formation is discussed. X-ray diffraction and electron diffraction results show that
the powders have the needed tetragonal perovskite structure. The band gap of KTN nanoparticles is determined to be 3.26 eV
from the optical absorption spectra.
相似文献
5.
Physics of the Solid State - The time changes of permittivity, damping and velocity of sound are studied for PbFe0.5Nb0.5O3 and PbFe0.5Nb0.5O3–7PbTiO3 single crystals in the electric fields... 相似文献
6.
Downward self‐polarization of lead‐free (K0.5Na0.5)(Mn0.005Nb0.995)O3 ferroelectric thin films on Nb:SrTiO3 substrate
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Hae Jin Seog Chang Won Ahn Shinuk Cho Kwang‐Eun Kim Chan‐Ho Yang Tae Yeong Koo Sun‐Young Lee Jong Pil Kim Ill Won Kim 《固体物理学:研究快报》2017,11(1)
Spontaneously appearing macroscopic polarization (self‐polarization) in ferroelectrics without an electrode or an external electric field would enable the freedom to design many ferroelectric heterostructures and devices. The (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) thin film was grown on Nb:SrTiO3 single‐crystal substrate and the resultant self‐polarization behavior due to strain relaxation was investigated. The lattice mismatch and difference in TEC between the KNMN thin film and the Nb:SrTiO3 substrate creates a compressive strain. The compressive strain gradient may be the main cause for the observed downward self‐polarization. The downward self‐polarization of the KNMN thin film can be explained by the strong inhomogeneous compressive strain caused by strain relaxation. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
7.
I. P. Raevskii V. V. Eremkin V. G. Smotrakov E. S. Gagarina M. A. Malitskaya 《Physics of the Solid State》2000,42(1):161-164
The cooling of Pb1?x BaxSc0.5Nb0.5O3 solid solutions with x≤0.04 leads to a spontaneous transition from a relaxor to a macrodomain ferroelectric state, accompanied by anomalous variation of the dielectric and optical properties of the material. As the barium content in the system increases, the relaxor state becomes more stable and eventually “freezes” at x≈0.05. The crystals with x=0.06 exhibited the appearance of a macrodomain ferroelectric phase induced both by an external electric field with a strength of 1.5 kV/cm and by an internal electric field formed in the course of dielectric aging. 相似文献
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J. Sigman H.J. Bae D.P. Norton L.A. Boatner 《Applied Physics A: Materials Science & Processing》2005,81(2):289-293
The dielectric response of K(Nb,Ta)O3 films grown on (001) MgAl2O4 (100) by pulsed laser deposition from a mosaic target of KTa0.63Nb0.37O3 and KNO3 has been examined. In particular, the effects of growth temperature (650–800 °C), growth pressure (1–100 mTorr O2), and annealing conditions on the tunability, dielectric constant, and dielectric losses in interdigitated capacitor device structures fabricated with these films are described. Annealing treatments lead to a reduction in the loss tangents for most of the films considered. Figure of merit calculations indicate that the best dielectric response (tunability=37%, tan =0.022) is achieved for films grown at 750 °C in an oxygen pressure of 100 mTorr and then annealing at 1000 °C for 2 h in air. 相似文献
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K. G. Abdulvakhidov I. V. Mardasova T. P. Myasnikova V. A. Kogan R. I. Spinko M. F. Kupriyanov 《Physics of the Solid State》2001,43(3):508-512
Crystals of PbSc0.5Nb0.5O3 are investigated by x-ray diffraction and optical spectroscopy. It is found that the phase transformations in PbSc0.5Nb0.5O3 are governed by two mechanisms: displacive ferroelectric phase transitions and consistent rotations of oxygen octahedra. 相似文献
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L. S. Kamzina I. P. Raevskii V. V. Eremkin V. G. Smotrakov 《Physics of the Solid State》2002,44(9):1754-1758
The optical properties of Pb0.96Ba0.04Sc0.5Nb0.5O3 (PBSN-4) and Pb0.94Ba0.06Sc0.5Nb0.5O3 (PBSN-6) single-crystal solid solutions were studied for the first time. It was shown that the spontaneous phase transition occurring in PBSN-4 with no electric field present is accompanied by a sharp minimum in optical transmission, which indicates the percolation nature of the transition. No sharp changes were observed in the temperature dependence of optical transmission in PBSN-6 single crystals with no electric field applied. However, a very weak electric field, ~0.4 kV/cm, is sufficient to induce the ferroelectric state in PBSN-6 single crystals. It was shown that the destruction of the induced ferroelectric state is a first-order phase transition which is accompanied by an anomalously narrow peak in the small-angle light scattering intensity (or by a minimum in optical transmission) and occurs through the percolation mechanism. 相似文献
11.
Yizhak Yacoby 《Zeitschrift für Physik B Condensed Matter》1978,31(3):275-282
First order Raman lines observed in the paraelectric phase of KTa0.94Nb0.06O3 are shown to be the result of odd symmetry microdistortions or fluctuations with a correlation length that extends to several unit cells. The possibilities that the lines result from impurity induced or disorder induced Raman scattering are considered and discarded. From simple theoretical considerations it is shown that the integrated intensity of distortion induced first order Raman lines, normalized by the corresponding phonon occupation numbers, is proportional to the average distortion intensity. This proportionality is independent of the correlation length of the distortion field provided it is larger than a certain minimum.Using this relation and the experimentally measured integrated intensity of the TO2 line we find that the average distortion intensity is proportional toT/(T
c—T). This result is compared to two models which qualitatively predict the existence of microdistortions or fluctuations in the paraelectric phase. The experimentally observed temperature dependence is found to be consistent with the defect induced fluctuations model and inconsistent with continuous phase transitions models. 相似文献
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Multilayered BaTiO3(BTO)/Bi0.5K0.5TiO3 (BKT) thin films have been fabricated on Pt/Ti/SiO2/Si substrates using a metalloorganic decomposition process. XRD investigation of the resultant BTO/BKT multilayered thin films shows that they retain a perovskite-related structure type. They also exhibit a well-defined, polarization–electric field hysteresis loop with a measured remnant polarization (2Pr) of 5 µC/cm2 at an applied electric field of 250 kV/cm. The measured dielectric constant and dielectric loss at 10 kHz is 470 and 0.07 respectively. These multilayer BTO/BKT films maintain an excellent fatigue-free character even after 109 switching cycles. The mechanism associated with the enhancement of the electrical properties of the synthesized BTO/BKT films is also discussed. 相似文献
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G.S. Brown L.R. Testardi J.H. Wernick A.B. Hallak T.H. Geballe 《Solid State Communications》1977,23(12):875-878
We have measured the Extended X-ray Absorption Fine Structure (EXAFS) spectra for superconducting thin films of Nb3Ge prepared at variable deposition temperature by sputtering and electron beam coevaporation. As the deposition temperature is varied from 1050 K to 875 K, the film structure changes continuously from the A15 phase to a quasi-amorphous phase. This amorphous phase is characterized by a mean Ge-Nb distance of 2.66 A, as compared to the A15 distance, 2.87 A. The mean coordination of the Ge sites is reduced from 12 to 8±2, and the mean square spread in Ge-Nb distances (thermal + spatial) has decreased by only 0.01 A2. 相似文献
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Alumina thin films were deposited on hot work tool steel AISI H11 at a growth temperature of 500 to 600 °C by plasma assisted chemical vapour deposition and were studied with respect to the structure and composition by X-ray diffraction and electron-probe microanalysis, respectively. The electrical power density at the cathode was varied from 2.7 to 6.6 W/cm2. Within the investigated process window the following characteristic phases could be identified: γ-alumina and α-alumina as well as mixtures thereof. The alumina phase formation was found to be strongly influenced by deposition temperature and electrical power density at the substrate. It is shown that constitution changes due to a reduction in substrate temperature can be avoided by increasing the electrical power density at the cathode, which leads to an increase in both ion flux and ion energy at the substrate surface. PACS 52.77.Dq; 68.55.Nq; 68.55.Ac; 61.10.Nz 相似文献
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Yanmin Huang Danping Shi Laijun Liu Guizhong Li Shaoying Zheng Liang Fang 《Applied Physics A: Materials Science & Processing》2014,114(3):891-896
Bi0.5Na0.5TiO3 (BNT)-doped BaFe0.5Nb0.5O3 (BFN) ceramics were synthesized by a two-step solid-state reaction. Temperature dependence of dielectric properties measured at different frequencies was investigated over broad temperature and frequency ranges. Impedance spectroscopy and universal dielectric response were employed to study the relaxation behavior and conductivity mechanism of the ceramics in a frequency range from 40 Hz to 100 MHz and a temperature range from 300 K to 800 K. The complex plane impedance data revealed the bulk and grain boundary contributions toward conductivity processes in the form of semicircular arcs. The high-temperature conductivity of ceramics is attributable to thermally activated second ionized oxygen vacancy. 相似文献
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《Physics letters. A》2001,288(1):45-48
The full potential linearized augmented plane wave method within the generalized gradient approximation was used to determine the tetragonal fine structure for PbFe0.5Nb0.5O3, i.e., the equilibrium configuration of B-site compound cations (Fe and Nb). It was found that the displacement of atom Fe along [001] direction is 0.022 nm and that of Nb is 0.0020 nm. The ferroelectric instability of complex compound PbFe0.5Nb0.5O3 is mainly coming from the displacement of atom Fe along [001] direction. 相似文献
19.
采用Sol-Gel工艺低温制备了Si基Bi3.25La0.75Ti3O12铁电薄膜.研究了退火温度对薄膜微观结构、介电特性与铁电性能的影响.500℃退火处理的Bi3.25La0.75Ti3O12薄膜未能充分晶化,晶粒细小且有非晶团聚,介电与铁电性能均较差.高于550℃退火处理的Bi3.25La0.75Ti3O12薄膜表面平整无裂纹,晶粒均匀,无焦碌石相或其他杂相,薄膜为多晶生长,具有较好的介电与铁电性能,4V电压下的漏电流密度低于2×10-8A/cm2.随退火温度升高,晶化程度的提升和晶粒尺寸的增大使薄膜的剩余极化增大而矫顽电场降低.600℃退火处理的Bi3.25La0.75Ti3O12薄膜显示了优于Bi4Ti3O12薄膜的铁电性能,其剩余极化Pr和矫顽电场Ec分别达到17.5μC/cm2和102kV/cm. 相似文献
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I. P. Raevskii V. V. Eremkin V. G. Smotrakov E. S. Gagarina M. A. Malitskaya 《Physics of the Solid State》1999,41(10):1678-1680
The degree of compositional order S of crystals of the complete series of solid solutions (1−x)PbSc0.5Nb0.5O3-xPbSc0.5Ta0.5O3 grown under identical conditions is determined by x-ray examination. The form of the dependence S(x) and the variations of S for different compositions, after high-temperature annealing, indicate that the concentration dependence of the compositional
order-disorder phase-transition temperature is close to linear in the given system of solid solutions.
Fiz. Tverd. Tela (St. Petersburg) 41, 1828–1830 (October 1999) 相似文献