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1.
Subrat K. Barik Ram N. P. Choudhary Prasanta K. Mahapatra 《Central European Journal of Physics》2008,6(4):849-852
The polycrystalline samples of Na1/2Y1/2TiO3 were prepared by the mixed-oxide method. A preliminary X-ray structural analysis was shown to exhibit the formation of a
single-phase compound with an orthorhombic structure. Microstructural analysis by scanning electron microscopy (SEM) exhibits
well defined grains distributed uniformly through out the sample suggesting the compactness and homogeneity of the sample.
Detailed studies of dielectric properties of Na1/2Y1/2TiO3 in a wide frequency range (102–106 Hz) at different temperatures (31–500°C) show a dielectric anomaly at 105°C, which may
be related to a ferroelectricparaelectric phase transition as suggested by hysteresis loop at room temperature. An ac conductivity
(σ
ac) of the material is mainly governed by the polaron hopping mechanism, which is also influenced by both frequency and temperature.
The activation energy was obtained from the plot of temperature with a.c. conductivity.
相似文献
2.
X.X. Wang X.G. Tang K.W. Kwok H.L.W. Chan C.L. Choy 《Applied Physics A: Materials Science & Processing》2005,80(5):1071-1075
(Bi1/2Na1/2)TiO3 ceramics (BNT) with 0–6 mol% of excess Bi2O3 are prepared by conventional solid-state sintering. The electrical properties of the samples are examined. The addition of excess Bi2O3 reduces the leakage current of BNT ceramics significantly, thus facilitating the poling process, and improves their piezoelectric properties slightly for certain amounts of added Bi2O3. BNT ceramics have very high dielectric constants and dissipation factors at low frequency and high temperature due to their high conductivity. Adding excess Bi2O3 to BNT ceramics affects their dielectric behavior and phase transition temperatures. Grain growth is suppressed by adding Bi2O3 and no second phase is observed for BNT ceramics with up to 6 mol% of excess Bi2O3 added. 相似文献
3.
Qiang Li Hairong Wang Huiqing Fan Mengmeng Xu Biaolin Peng Changbai Long Xiao Liu 《Applied Physics A: Materials Science & Processing》2014,114(2):551-558
La2O3 (2 wt%)-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 (abbreviated as BNBT6) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction. X-ray diffraction (XRD) patterns indicated that La2O3 has diffused into the lattice of BNBT6 ceramics and formed a solid solution with a pure perovskite structure. Addition of La2O3 decreased the piezoelectric properties and electrical conductivity. It was used to study the electrical conductivity of the La2O3-doped BNBT6 lead-free piezoelectric ceramics combined with electrical modulus and impedance plots at the temperature range over 788–873 K. The values of activation energy derived from the electrical impedance and modulus were found to be 0.51 and 0.50 eV, respectively. The discrepancy between activation energy of relaxation frequency and the activation energy (0.25 eV) of dc electrical conductivity might have been due to a short-range migration or hopping of single ionized oxygen vacancy and a long-range migration or hopping of charge carriers over the whole disordered system, respectively. 相似文献
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The luminescence properties of K(1/2)Bi(1/2)TiO(3):Pr(3+) and Na(1/2)Bi(1/2)TiO(3):Pr(3+) powders are investigated in the temperature range 10-600 K. The experimental data are interpreted on the basis of metal-to-metal charge transfer processes and by considering Bi(3+)-to-Pr(3+) sensitization effects. 相似文献
6.
《Current Applied Physics》2009,9(2):380-383
The polycrystalline sample of Na1/2Dy1/2TiO3 ceramic was prepared by a standard high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of single-phase (with minor secondary phase) compound in the orthorhombic (distorted tetragonal) crystal system at room temperature. Study of surface morphology by scanning electron microscope exhibits uniform distribution of rectangular/cubical grains with less voids. The elemental composition of the prepared compound was confirmed by energy dispersive X-ray spectroscopy microanalysis. Detailed studies of dielectric properties exhibit a dielectric anomaly at 94 °C suggesting a possible ferroelectric–paraelectric phase transition in the compound. The activation energy (Ea), calculated from the temperature dependence of ac conductivity plot, was found to be small (∼0.1 eV) in low temperature and large (∼0.5 eV) in high temperature region. 相似文献
7.
Polycrystalline ceramic samples of pure and 50% La substituted BiFeO3 have been prepared by standard solid state reaction method using high purity oxides and carbonates. The formation of the single phase compound as well as its chemical analysis has been checked by X-ray diffraction and energy dispersive X-ray microanalysis (EDAX) techniques. A better agreement between observed and calculated X-ray powder diffraction patterns was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group R3c. The lattice parameters in both the cases have been refined but the over-all structure remains the same. The microstructural studies have been carried out using scanning electron microscopy (SEM). Modulated differential scanning calorimetry (MDSC) has been used to detect the Neel/transition temperature in the compounds. The activation energies calculated from log σ vs 1/T curve are 0.81 eV and 1.13 eV respectively. Vibrating sample magnetometer (VSM) has been used to study the magnetic behaviour of the compounds. It has been observed that by 50% La substitution the insulating behaviour of the material has been improved and showing the antiferromagnetic to weak ferromagnetic behaviour. 相似文献
8.
M. Zannen M. Dietze H. Khemakhem M. Es-Souni 《Applied Physics A: Materials Science & Processing》2014,117(3):1485-1490
Polycrystalline lead-free (Na1/2Bi1/2)TiO3 (NBT) ferroelectric thin films doped with 1 mol% of rare earth (RE) elements are processed on Pt-terminated silicon substrates using a solution deposition method. The thin films that exhibit single-phase perovskite structure show photoluminescence properties with highest intensities in the wavelength range between 700 and 850 nm, depending on RE element. The ferroelectric properties of the pure NBT film (P r: 20.5 µC cm?2, E c: 150 kV cm?1) are somewhat decreased for the doped films, which is ascribed to decreasing of the number of Bi lone pairs through the substitution of Bi with RE elements in the perovskite lattice. 相似文献
9.
I. P. Aleksandrova Yu. N. Ivanov A. A. Sukhovskiĭ S. B. Vakhrushev 《Physics of the Solid State》2006,48(6):1120-1123
The 23Na NMR spectra of a Na1/2Bi1/2TiO3 crystal are studied at frequencies of 79.4 and 15.7 MHz in the temperature range 150–720 K. It is revealed that, at all temperatures, the crystal contains regions with a nearly cubic matrix and polar clusters. The temperature dependence of the local distortion of the Na environment in the clusters is determined. The dynamics of the reorientation of the local cluster polarization in the tetragonal and trigonal NBT phases is analyzed. 相似文献
10.
用固相反应法制备了Na0.25K0.25Bi0.5TiO3(NKBT50)陶瓷,研究了该陶瓷在室温至400℃温度范围内的介电性能.发现该陶瓷的介电温谱与烧结气氛、极化状态有关.在空气中烧结的未极化样品在70℃附近存在介电和损耗峰,而极化后及在氧气氛中烧结的样品并不存在该介电、损耗峰.分析认为70℃的介电和损耗峰与氧空位形成的缺陷偶极子的极化弛豫有关.热激电流显示,陶瓷的去极化温度为225℃,与此相对应的介电、损耗峰也与氧空位有关. 相似文献
11.
X.X. Wang H.L.W. Chan C.L. Choy 《Applied Physics A: Materials Science & Processing》2005,80(2):333-336
(Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT-6) with simultaneous addition of 0.5 mol% CeO2 and 0.25, 0.5 and 0.75 mol% La2O3, respectively, was prepared by a conventional ceramic fabrication technique. An addition of 0.5 mol% CeO2 together with 0.5 mol% La2O3 enhanced the piezoelectric and dielectric constant of BNBT-6 ceramics significantly. At room temperature, this composition exhibits a high piezoelectric constant (d33=162×10-12 C/N) and relatively low dielectric loss (cos=2.0%) at 1 kHz. X-ray diffraction pattern shows that the coexistence of tetragonal and rhombohedral phases in the BNBT-6 composition was not changed by adding CeO2+La2O3, and they diffused into the BNBT lattice during sintering. SEM observation indicates that a small amount of CeO2+La2O3 almost does not affect the microstructure. PACS 77.65.Bn; 77.84.Dy; 77.22.-d 相似文献
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The effect of lanthanum substitution on the structural, dielectric and piezoelectric properties of lead calcium titanate (PCT) ceramics is studied. Samples with compositional formula Pb0.76? x La x Ca0.24Ti0.98Mn0.02O3 (PLCT) (x?=?0–0.08, in steps of 0.02) were prepared by the conventional dry ceramic technique. Phase and structural analysis was carried out using XRD and SEM respectively. X-ray analysis confirmed the formation of single-phase compound with tetragonal crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. The Curie temperature (T C) and tetragonality (c/a) was found to decrease with increase in lanthanum content. The Curie temperature was also confirmed from the thermal-expansion behaviour of the sintered samples. Piezoelectric coefficients (d 33, d 31, g 33, g 31, g h, d h, k t and k p) were measured at room temperature. From this study it is found that La3+ substitution helps in the improvement of electro-mechanical anisotropy. 相似文献
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A. V. Pavlenko S. I. Shevtsova A. T. Kozakov L. A. Shilkina A. A. Pavelko L. A. Reznickenko 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(7):782-785
Ceramic samples of lead ferroniobate (PFN) having a rhombohedral symmetry at room temperature are obtained. Their ferroelectric and magnetic properties in the vicinity of the antiferromagnetic and ferroelectric phase transition temperatures are investigated. The electrophysical parameters of the polarized ceramic are presented. By means of electron-probe microanalysis, the number of inclusions of Fe-containing impurity phases (??0.2 vol %) is revealed to be several times higher than that in grains of the PFN ceramics. It is suggested that the above could be caused by the magnetic properties of PFN at room temperature. 相似文献
16.
Xiang Liu Xue-Peng Yin Qing-Ming Chen Hui Zhang Shao-Chun Zhang 《Applied Physics A: Materials Science & Processing》2014,116(4):1853-1856
La2/3Ba1/3MnO3:Ag0.04 (LBMO:Ag0.04) thin films were prepared on single crystalline (001)-orientated LaAlO3 substrates by pulsed laser deposition technique. Thermal annealing with temperatures of 780, 800 and 820 °C has been investigated to improve electrical properties of the films. All the samples are shown along the (00l) orientation in rhombohedral structure with \( R\overline{3} c \) space group. With thermal annealing temperature increasing, insulator–metal transition temperature (T p) and resistivity at T p ( \( \rho_{{T_{\text{p}} }} \) ) of the epilayer reach optimal value of 288 K and 0.03 Ω·cm, respectively. The electrical properties improvement of the LBMO:Ag0.04 films is due to an improved film crystallization, oxygen balance and photon scattering suppression. The fitting curves show that the region of ferro-magnetic metallic (FM, T < T p) is fitted with grain/domain boundary, electron–electron and magnon scattering mechanism, as well as the region of para-magnetic insulating (PI, T > T p) is fitted with adiabatic small polaron hopping mechanism. 相似文献
17.
Yang Qiu Songliu Yuan Zhaoming Tian Liang Chen Chuanhui Wang Hanning Duan Kai Guo 《Applied Physics A: Materials Science & Processing》2012,107(2):379-383
Single phase Bi1/2Na1/2Cu3Ti4O12 (BNCTO) ceramics with different grain sizes (1.4–4.3 μm) are prepared by a modified Pechini method to investigate their giant
dielectric and nonlinear electrical behaviors. The results show that the giant dielectric and nonlinear electrical behaviors
are strongly dependent on grain size. With the increment of grain size, the dielectric constant increases monotonically from
14110 (for 1.4 μm sample) to 36183 (for 4.3 μm sample) at 1 kHz, in accompaniment with the breakdown voltage reducing from
112.5 to 43.2 V/mm and the nonlinear coefficient reducing from 4.9 to 3.4. On the basis of the internal barrier layer capacitor
(IBLC) model and the IBLC model of Schottky-type potential barrier, an interpretation of the grain size effect on the giant
dielectric and nonlinear electrical behaviors is presented. 相似文献
18.
J. Fuentes J. Portelles A. Pérez M. D. Durruthy-Rodríguez C. Ostos O. Raymond J. Heiras M. P. Cruz J. M. Siqueiros 《Applied Physics A: Materials Science & Processing》2012,108(3):733-738
We report the results of studies of rectifying behavior, positive magneoresistance (MR), the charge-transport mechanism and the effect of an electric field on a ZnO (n)/La0.5Pr0.2Sr0.3MnO3 (LPSMO) (p)/SrNb0.002Ti0.998O3 (SNTO) (n) heterostructure comprising two p–n junctions fabricated using the pulsed laser deposition technique. The heterostructure exhibits rectifying behavior over a wide temperature and field range having hysteresis in I–V behavior (forward bias) due to the tunneling of charge carriers. It is also observed that, depending on the nature of the electric field bias to n-type ZnO and SNTO, the junction resistance becomes modified, which has been explained on the basis of spin injection in the heterostructure. The observation of unconventional positive MR at room temperature has been justified on the basis of interface effects and the reduction in barrier height obtained using fitting of the I–V data by a thermionic emission model. 相似文献
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Mengwu Huo 《中国物理 B》2022,31(10):107401-107401
Superconductivity has been realized in films of La1-xSrxNiO2. Here we report synthesis and characterization of polycrystalline samples of La1-xSrxNiO3 and La1-xSrxNiO2 (0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La1-xSrxNiO3 are paramagnetic metal and La1-xSrxNiO2 exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La1-xSrxNiO2. The absence of superconductivity in bulk La1-xSrxNiO2 may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen. The effect of interface in films of La1-xSrxNiO2 may also play a role for superconductivity. 相似文献