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1.
The transverse laser induced thermoelectric voltage effect has been investigated in tilted La0.5Sr0.5CoO3 thin films grown on vicinal cut LaAlO3 (1 0 0) substrates when films are irradiated by pulse laser at room temperature. The detected voltage signals are demonstrated to originate from the transverse Seebeck effect as the linear dependence of voltage on tilted angle in the range of small tilted angle. The Seebeck coefficient anisotropy ΔS of 0.03 μV/K at room temperature is calculated and its distorted cubic structure is thought to be responsible for this. Films grown on a series of substrates with different tilted angles show the optimum angle of 19.8° for the maximum voltage. Film thickness dependence of voltage has also been studied.  相似文献   

2.
A series of Pr0.5Sr0.5MnO3 (PSMO) films with various thickness were epitaxially grown on substrates of (0 0 1)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT), LaAlO3 (LAO) and SrTiO3 (STO), and (0 1 1)-oriented STO using pulse laser deposition. Influence of epitaxial growth on phase competition was investigated. A ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition upon cooling is present in both largely compressed situations deposited on LAO (0 0 1) and tensile cases deposited on STO (0 0 1) but absent in little strained films grown on LSAT (0 0 1), indicating that the antiferromagnetic insulating state is favored by strains. On the other hand, the 400 nm films deposited on (0 1 1)-oriented STO as well as LAO substrates show FMM-AFI transition. These results reveal that both the orientation of epitaxial growth and substrate-induced strain affect the FMM-AFI transition.  相似文献   

3.
We present in this paper the experimental results of photoluminescence spectra of Ba0.5Sr0.5TiO3 ceramics. An emission band centered at about 920 nm has been observed at room temperature. When we change the amount of oxygen vacancies in these samples by thermal treatment, these samples show an enhancement of luminescence. Our experimental results indicate that the origin of the photoluminescence is related to the oxygen vacancies in these samples.  相似文献   

4.
邓杨  王如志  徐利春  房慧  严辉 《物理学报》2011,60(11):117309-117309
采用基于密度泛函理论(DFT)的第一性原理计算研究了 (Ba0.5Sr0.5)TiO3 (BST) 晶体在高压下的电子结构及能带变化行为. 研究结果发现,随着压强的增加,BST能带间隙先增加,在压强为55 GPa时达到最大值,然后减小,这些有趣的结果将有助于开发与设计新的BST铁电器件. 进一步地,通过电子态密度和密度分布图的研究分析可知:在低压区域(055 GPa),则是出现的离域现象占主导(电子的离域作用超过键态的作用),从而使带隙减小. 关键词: 钛酸锶钡 第一性原理 高压 能带间隙  相似文献   

5.
The microwave dielectric properties of CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics were investigated with a view to their application in microwave devices. CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics exhibited no significant variation of phase with sintering temperature. By adding 0.75 wt.% CuO, a dielectric constant of 20.07, a quality factor (Q × f) of 63,000 GHz, and a temperature coefficient of resonant frequency τf (−77.0 ppm/°C) were obtained when La2.98/3Sr0.01(Mg0.5Sn0.5)O3 ceramics were sintered at 1500 °C for 4 h.  相似文献   

6.
The ablation process of La0.5Sr0.5CoO3 by a spatial uniform 248 nm excimer laser beam has been characterized. Ablation rates, changes in the target surface morphology and composition have been studied as a function of the laser fluence. The dependence of the ablation rate on the laser fluence has been explained by a model based on plasma absorption. The threshold fluence for complete dissociation of the surface has been determined and is found equal to 0.7 J/cm2. Above this threshold, a steady-state target surface condition is obtained within 30 pulses. Below the threshold fluence, CoO nuclei form, which have a pronounced effect on the target composition and morphology. In addition, ellipsometric and reflectance spectra have been measured in the photon energy range of 1.8 to 5.0 eV.  相似文献   

7.
Thin films of barium strontium titanate (Ba1−xSrx TiO3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible SO interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm−1, which is characteristic of an OSC stretching and reveals the modification of the BSTO thin film by the coupling of the O of the BSTO with the S of the mercapto compound. All the modification using mercapto compounds is through sulfur to the BSTO thin film. MHDA SAM on BSTO thin film was chemically derivatized using APS shown by XPS and FT-IR. The SAMs modified phase shifters showed an improvement in performance with respect to those phase shifters fabricated with standard methods.  相似文献   

8.
杨天应  蒋书文  李汝冠  姜斌 《中国物理 B》2012,21(10):106801-106801
Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators(FBARs) based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3(BST) films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias( 45 V) while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum(Mo) as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.  相似文献   

9.
杨春燕  张蓉  张利民  可祥伟 《物理学报》2012,61(7):77702-077702
采用基于第一性原理密度泛函理论的平面波赝势方法,对0.5NdAlO3-0.5CaTiO3晶体进行结构优化,并对其能带结构,态密度和光学性质进行了理论计算.结构优化后晶格参数与实验数据相符合,误差小于1%;能带计算结果表明0.5NdAlO3-0.5CaTiO3为间接带隙,带隙值为0.52eV;费米面附近的能带由Nd-4f,O-2p,Nd-4p,Al-3p,Ti-4d层的电子态密度确定.同时也计算了该结构的介电函数,反射率和复折射率等光学性质.  相似文献   

10.
王秀章  刘红日 《物理学报》2007,56(3):1735-1740
通过sol-gel法在Si (111) 基片上分别制备了LaNiO3(LNO)底电极和LaNiO3/La0.3Sr0.7TiO3 (LNO/LSTO)底电极.然后采用sol-gel 方法,在两种衬底上分别制备了Pb (Zr0.5Ti0.5)O3 (PZT)铁电薄膜.XRD分析表明,两种PZT薄膜均具有钙钛矿结构,且在LNO底电极上的PZT薄膜呈(100) 择优取向,而在LNO/LSTO底电极上的PZT薄膜呈随机取向.铁电性能测试表明,相对LNO衬底上制备的PZT薄膜,在LNO/LSTO底电极上制备的PZT薄膜的剩余极化强度得到了有效的增强,同时矫顽场也增大.介电常数和漏电流的测试表明,LNO/LSTO底电极上制备的PZT薄膜具有大的介电常数和漏电流. 关键词: PZT薄膜 铁电性 漏电流 0.3Sr0.7TiO3')" href="#">La0.3Sr0.7TiO3  相似文献   

11.
赵静波  杜红亮  屈绍波  张红梅  徐卓 《物理学报》2011,60(10):107701-107701
研究了在铌酸钾钠基陶瓷中,A位等价与非等价取代对陶瓷极化温度和极化电场的影响,结果表明:A位等价取代的陶瓷对极化温度和极化电场没有强烈依赖性,可以使极化足够充分,能有效提高铌酸钾钠基陶瓷的压电性能;相反,A位非等价取代的陶瓷对极化温度和极化电场敏感,容易击穿,极化不充分,限制了铌酸钾钠基陶瓷的压电性能. 关键词: 铌酸钾钠 极化 压电  相似文献   

12.
Binary (ZnO)0.5(P2O5)0.5 glasses doped with Eu2O3 and nanoparticles of Gd2O3:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)0.5(P2O5)0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na2O-SiO2 glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu3+ ions leading to improved Eu3+ luminescence from such glasses. Based on the decay curves corresponding to the 5D0 level of Eu3+ ions in both Gd2O3:Eu nanoparticles incorporated as well as Eu2O3 incorporated glasses, a significant clustering of Eu3+ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)0.5(P2O5)0.5 glass doped with Gd2O3:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu3+ ions. Poor energy transfer from the defect centres to Eu3+ ions in Gd2O3:Eu nanoparticles doped (ZnO)0.5(P2O5)0.5 glass has been attributed to effective shielding of Eu3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu3+ ions.  相似文献   

13.
刘立英  王如志  朱满康  侯育冬 《中国物理 B》2013,22(3):36401-036401
The effects of La doping on the ferroelectric properties of 0.92Na0.5Bi0.5TiO3-0.08BaTiO3(NBT-BT) solid solution have been studied both experimentally and theoretically.The experimental results show that an abnormal ferro-toantiferroelectric phase transition is induced by La doping in NBT-BT.The first-principles calculations indicate that La3+ cations selectively substitute for the A site in NBT-BT as donors.Furthermore,the computed binding energy reveals that La cations is most likely to substitute Ba 2+or Na+,not Bi3+,at A site as donors in NBT-BT,as supported by our Raman spectra.The ferro-to-antiferroelectric phase transition of La-doped NBT-BT is believed to originate from the lattice aberrance and redistribution of valence electrons,thus strengthening the bonding of A-O,enhancing the hybridization between the A cation d orbital and O 2p orbital,and resulting in the deflection of the polar direction of NBT-BT lattice.  相似文献   

14.
Zinc phosphate glasses doped with Gd2O3:Eu nanoparticles and Eu2O3 were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P2O5 glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu3+ ions has been observed when Eu2O3 is incorporated in ZnO-P2O5 glasses. Lack of energy transfer from these defect centres to Eu3+ in Gd2O3:Eu nanoparticles doped ZnO-P2O5 glass has been attributed to effective shielding of Eu3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu3+ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd2O3:Eu nanoparticles or Eu2O3 incorporation.  相似文献   

15.
Epitaxial Pr0.5Ca0.5MnO3 films have been synthesized on (0 0 1) SrTiO3 substrate using a chemical solution deposition technique and two-step post-annealing process. The zero field resistivity of the films shows semiconducting behavior and a characteristic of charge ordering is observed at 230 K. The resistivity of the 10 nm film did not show any effect with the magnetic field. However, melting of charge ordering was observed for the 120 nm film at an applied magnetic field of 4 T. Large decrease in the resistivity of the 120 nm film (<100 K) resulted in magnetoresistance of nearly −100% at 75 K.  相似文献   

16.
The co-doping of Li+ and Al3+ ions drastically enhances the luminescence of cubic Eu2O3. The integrated emission intensity of 5D07FJ bands (J=1-4) at 580-710 nm increases by a factor of about 6.7 in the co-doped Eu2O3 compared to the un-doped Eu2O3. In order to confirm that the co-doped ions were actually incorporated into the host lattice, the structural characteristics were studied using Raman spectroscopy, XPS, XRD, photoluminescence lifetime, and an SEM. These analyses consistently indicate a certain structural evolution in their results with an increase in the co-doping concentration. Variations in the crystal structure, the crystal morphology, and the intensity variation of the Raman modes at 465 and 483 cm−1 are presented as the evidences showing the incorporation of the co-doped ions into the host. The luminescence enhancement is discussed in terms of concentration quenching, reduction of defect sites, and the modification of the local symmetry of the Eu3+ ions, especially in the inversion symmetry sites.  相似文献   

17.
Ho3+ doped Ba0.65Sr0.35TiO3 (BST) nanocrystals was prepared by sol-gel method. The structural and morphological properties of the nanocrystals were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absorption spectrum, photoluminescence spectrum and fluorescence time decay curve were measured at room temperature. Based on the Judd-Ofelt (J-O) theory, the J-O intensity parameters Ωt (t=2, 4, 6) of Ho3+ doped BST nanocrystals were calculated to be 0.67×10−20 cm2, 1.11×10−20 cm2 and 1.09×10−20 cm2, respectively. The emission probabilities, radiative lifetimes and branching ratios of the different Ho3+ transitions were also determined. The emission cross sections of the important intermanifold transitions 5F4,5S25I8, 5F55I8 and 5F45I7 have been calculated from the luminescence spectrum. The room temperature fluorescence lifetime of the 5S25I8 transition for Ho3+ in BST nanocrystals was measured and the radiative quantum efficiency was estimated to be 61.9%.  相似文献   

18.
马玉彬 《物理学报》2009,58(7):4976-4979
研究了氧空位对La0.5Ca0.5MnO3 (LCMO)多晶块材的电输运和磁性质的影响. 随着氧空位的增加, 样品在高温段的电阻率一直增加, 并满足绝热小极化子模型, 而低温段的电阻率先下降后上升, 并出现明显的dR/dT>0的行为, 直至最后变为绝缘的. 氧空位的增加抑止了反铁磁相的出现, 使得脱氧的LCMO样品不发生反铁磁转变, 进一步增加氧空位则会抑制铁磁相. 关键词: 0.5Ca0.5MnO3')" href="#">La0.5Ca0.5MnO3 反铁磁相变 铁磁相变 脱氧  相似文献   

19.
The microwave dielectric properties of La1-xBx(Mg0.5Sn0.5)O3 ceramics were examined with a view to their exploitation for mobile communication. The La1-xBx(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La0.995B0.005(Mg0.5Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. A maximum apparent density of 6.58 g/cm3, a dielectric constant (εr) of 19.8, a quality factor (Q × f) of 41,800 GHz, and a temperature coefficient of resonant frequency (τf) of −86 ppm/°C were obtained for La0.995B0.005(Mg0.5Sn0.5)O3 ceramics that were sintered at 1500 °C for 4 h.  相似文献   

20.
The microstructures and the microwave dielectric properties of the (1 − x)(Mg0.95Co0.05)TiO3x(Na0.5La0.5)TiO3 ceramic system were investigated. Two-phase system was confirmed by the XRD patterns and the EDX analysis. A co-existed second phase (Mg0.95Co0.05)Ti2O5 was also detected. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. A new microwave dielectric material 0.88(Mg0.95Co0.05)TiO3–0.12(Na0.5La0.5)TiO3, possessing an excellent combination of dielectric properties: εr  22.36, Q × f  110,000 GHz (at 9 GHz), τf  2.9 ppm/°C), is proposed as a candidate dielectric for GPS patch antennas.  相似文献   

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