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Temperature-dependent dielectric response of (1-x)PVDF/(x)BaTiO3 nanocomposite films
摘要： The PVDF/BaTiO3 nanocomposite films were prepared by solution casting method by using dimethylformamide as solvent. The dielectric constant and loss tangent of the PVDF and PVDF/BaTiO3 composites have been determined as functions of frequency (20 Hz to 2 MHz) and temperature (80 to 425 K). A significant enhancement in dielectric constant ε' is observed in composite samples. Tangent loss factor (tan δ) is maximum at lower frequencies due to interfacial polarization. In composite samples owing to the synthesis process, there is a phase transition in PVDF from α to β which results in the formation of dipolar relaxation. The dipolar nature of both the PVDF and PVDF/BaTiO3 nanocomposites is arrested below 200 K. The activation energy values (0.43- 0.69 eV) associated with tan δ peak in the region 200 – 270 K are in agreement with the activation energy associated with a dipolar relaxation process. The relaxation time (τ) decreases with increasing BaTiO3 filler content while the number density of dipoles increases from 4.06×1021 cm-3 for pristine PVDF to 6.62×1023 cm-3 for (0.5)PVDF/(0.5)BaTiO3 composite and confirms a significant amount of dipolar relaxation in PVDF/BaTiO3 composites.
关键词： dielectric relaxation,activation energy,dielectric constant,PVDF/BaTiO3 nanocomposites
更新于2025-11-14 17:28:48
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Role of Yb3+ ion on the evaluation of energy transfer and cross-relaxation processes in Gd2Ce2O7: Yb3+, Er3+ phosphors
摘要： Energy transfer (ET) and cross-relaxation (CR) processes play significant roles in regulating emitting colors and intensity of upconversion (UC) materials. Calculating the coefficients in ET and CR processes can provide visual descriptions for evaluating the UC luminescence properties. Here, we find that those ET and CR processes are responsible for the color-tunable properties in Gd2Ce2O7: Yb3+, Er3+ phosphors. By solving the rate equation, mathematical expressions are established to calculate the ET and CR coefficients based on the experimental UC spectra and lifetimes. The results are benefit to evaluate the efficiencies of ET and CR processes in quantization in different Yb3+ ion concentrations doped samples. The coefficients of ET process arise from 1.05 to 7.93 × 1017 cm3s?1 while those of CR process increase from 2.69 to 72.01 × 1017 cm3s?1 with increasing the Yb3+ ion concentration, which suggest that the CR and ET processes are efficient in Gd2Ce2O7 host. Furthermore, potential temperature sensing properties are also evaluated according to the fluorescence intensity ratio of 2H11/2 and 4S3/2 levels and the maximal sensitivity (S) is achieved about 0.00337 K?1 at 503 K. This work provides an insight into the evaluation of those UC processes and reveals the capacity in color-tunable and temperature sensing aspects.
关键词： Upconversion,Mathematical expression,Cross-relaxation,Temperature sensing,Energy transfer
更新于2025-11-14 17:03:37
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Study on Charge transportation and scaling behavior of CsPbI3 microwires
摘要： Cesium lead iodide (CsPbI3) has been prepared by a new experimental hazard free precipitation technique. X-ray diffraction spectra have been interpreted with Rietveld refinement which assures the orthorhombic phase of CsPbI3. Energy dispersive X-ray fluorescence spectra confirms the formation of ternary compound. Orthorhombic to cubic phase transition has been studied by observing hysteresis loop in R(T)-T plot for forward-reverse temperature scan. The intra-grain and inter-grain contribution of CsPbI3 to dielectric relaxation has been accounted by fitting the complex impedance plot (Cole-Cole plot). The value of FWHM in Z″(ω)-lnf or M″(ω)-lnf plot is greater than 1.141 decades which reveals the non-Debye type relaxation within material. The broad relaxation peak signifies that there is a distribution of relaxation time over a mean value. Moreover, Z″ & M″ have been plotted in scaled coordinate to check whether the distribution of relaxation time is temperature dependent or not. The frequency dependent relative permittivity represents the decreases of polarizations with frequency which have been successfully analyzed by Koop’s theory. Here, activation energies are equal for different formalism, suggests that the same type charge carriers involved in conduction as well as relaxation process. Ac conductivity has been interpreted by using Jonncher’s power law and frequency exponent (n) increases with temperature which suggests the presence small polaron hopping mechanism.
关键词： Joncher’s power law,dielectric relaxation,Rietveld,Hysteresis,Cole-Cole plot,CsPbI3 micro-wire
更新于2025-09-23 15:23:52
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Effect of Macro-scale Mechanical Stress of Silicon Wafer on Room Temperature Photoluminescence Signals
摘要： Mechanical stress was applied to single side polished and double side polished Si wafers in polypropylene wafer containers for different localized stress levels and durations. Room temperature photoluminescence (RTPL) spectra from Si wafers were measured before and after applying localized mechanical stress. Significant changes (up to 26% increase) in RTPL intensity were measured from areas under different stress levels even 1 year after the fixtures for mechanical stress generation were removed. Significant effects of localized mechanical stress on RTPL intensity variations were measured up to 49 days after the fixture removal. Nearly fully relaxed RTPL signatures for localized mechanical stress were measured 450 days after the fixture removal. RTPL intensity is found to be very sensitive to the externally applied macro-scale mechanical stress of Si wafers and residual (or memorized) internal stress even after removal of fixtures for external mechanical stress generation.
关键词： Silicon,room temperature photoluminescence,stress relaxation,mechanical stress
更新于2025-09-23 15:23:52
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Low-frequency dielectric spectroscopy and distinct relaxation modes in smectic phases of liquid crystal dimers
摘要： Low-Frequency (LF~20Hz–10MHz) ac field response and relaxation modes are investigated in layered liquid crystalline (LC) smectic phases exhibited by Hydrogen bonded dimers, viz., nOnBA:MA:nOBA’s with sort spacer moiety and long flexible end chains for n=10,11 and 12. Permittivity (ε') and loss (ε'') determined from capacitance and loss factor. Phase transition temperatures (Tc) are determined. Intra-molecular aromatic interaction and storage capacity are evinced by hysteresis behavior. Data of loss ε''(ω) and permittivity ε'r(ω) recorded in smectic phases infers non-Debye type of asymmetric dispersion. Multiple loss peaks in ε''(ω) is argued to involve distinct time scaled relaxations. Relaxation analyzed by Cole-Davidson method. Re-orientation of longitudinal dipole moment μ to the field analyzed. μ is resolved by rigid core, intra-molecular repulsive and flexible end-chain components. Observed distinct time scale response confirms dipolar components. Trends of relaxation frequency, activation energy, loss maxima, dielectric strength and distribution parameter are analyzed in device perspective. Relaxation and order director fluctuations analyzed. ODF suggest the device utility in high temperature smectic phases far away from critical fluctuations.
关键词： Order Director Fluctuations,Relaxation,Permittivity,Resolved dipole moment,Activation energy,Reorientation,Loss
更新于2025-09-23 15:23:52
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A comprehensive study on the interface states in the ECR-PECVD SiO2/p-Si MOS structures analyzed by different method
摘要： The electrical properties of SiO2/p-Si films deposited by ECR-PECVD were studied at different frequencies (100-1 MHz) and gate voltages (-6–3 V). Results showed a frequency dispersion of C-Vg and G/ω-Vg. With increasing frequency, the capacitance and conductance are strongly decreased. An apparent peak in the depletion regime of the G/ω-Vg plots can be attributed to the existence of density Nss at Si/SiO2. The (Nss)value vary from 1.5 × 10^12 to 0.5 × 10^11 eV^-1 cm^-2, it has been determined by High-Low frequency capacitance technic. The Nss- Vg curve presents a peak at about -3 V, suggesting the presence Nss between the (Si)/SiO2 interface. Hill and Coleman method shows that the Nss decreases with increasing frequency which explains the high value of capacitance at low frequency. The Nss and their relaxation time τ by the conductance method ranged from 1.8 × 10^13 to 1.37 × 10^11 eV^-1 cm^-2 and 5.17 × 10^-7 to 8 × 10^-6 s, in the range (0.189-Ev) and (0.57- Ev) eV, respectively. The Nss was responsible for the non-ideal behavior of C-Vg and G-Vg leading to the breakdown of such device. Comparing the three method results show that parallel conductance is very precise and accurate.
关键词： Capacitance method,Relaxation time,Frequency,Interface states,Metal/Oxide/Semiconductor (MOS),Conductance method
更新于2025-09-23 15:23:52
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Comparison the electron momentum and energy relaxation process in wurtzite GaN, InN and AlN by Monte Carlo method
摘要： At present, both transient and steady transport properties of III-V nitride semiconductors are researched, however, few research concerns about the momentum and energy relaxation process, which will be important during device designing. In order to clarify the fundamental physical process of the relaxation phenomenon, both momentum and energy relaxation process in wurtzite GaN, InN and AlN are studied with the help of classic three valleys Monte Carlo method. Our goal is to understand the relationship of relaxation rate with electric field, temperature and clarify the role of scattering mechanisms during momentum and energy relaxation process. The research shows that when the electric field and temperature are different, the main momentum and energy relaxation mechanisms may be different. For the lower effective mass in the lowest valley for InN, the electrons are more easily accelerated by electric field and scattered into the satellite valleys. The momentum relaxation time is much lower than that of energy relaxation time, the reason is that nearly all scattering mechanisms will relax momentum, but only polar optical phonon and inter-valley scattering relax electron energy. The research here can be used for construct the relaxation model or as a guide for device design.
关键词： Monte Carlo,III-V nitride,Electron momentum and energy relaxation
更新于2025-09-23 15:23:52
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Suitability of Raman Spectroscopy for Assessing Anisotropic Strain in Thin Films of Doped Ceria
摘要： A protocol for characterizing relaxation of anisotropic strain in thin films of 10 mol% Eu- or Sm-doped ceria is described. The method is based on comparison of Raman spectra and X-ray diffraction patterns from substrate-supported films, displaying in-plane compressive strain (initial state), with analogous data from 2 mm diameter self-supported films (i.e., membranes), prepared by partial substrate removal (final state). These membranes are found to be relaxed, i.e., approximately unstrained, but with increased unit cell volume. The effective (i.e., 2-state) Grüneisen parameter of the F2g Raman active mode for these films is calculated to be 0.4 ± 0.1, which is ≈30% of the literature value for the corresponding ceramics under isostatic pressure. On this basis, it is found that the observed red-shift of the F2g mode frequency following isothermal strain relaxation of the doped ceria thin films cannot be determined solely by the increase in average unit cell volume. The study presented here may shed light on the suitability of Raman spectroscopy as a technique for characterizing strain in lanthanide-doped ceria thin films.
关键词： doped ceria,Raman spectroscopy,Grüneisen parameter,anelastic relaxation
更新于2025-09-23 15:23:52
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Variable-range-hopping conduction and polaron dielectric relaxation in Cu and Nb co-doped BaTiO3
摘要： BaTi0.7(Cu0.1Nb0.2)O3 ceramic was prepared using a solid-state method and its structure, valence states, conduction mechanism and dielectric properties were investigated in detail. A fine-grained microstructure and a distorted pseudo-cubic perovskite structure were confirmed by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray photoelectron spectroscopy analysis suggested that Cu in BaTi0.7(Cu0.1Nb0.2)O3 was polyvalent but the valence states of Ti and Nb were invariable. Mott’s variable-range-hopping (VRH) conduction was observed. The two colossal dielectric constant plateaus in low- and high-temperature ranges were ascribed to the electrode and grain boundary responses, respectively. The VRH model described the low-temperature relaxation well, indicating that the dielectric relaxation was a polaron relaxation rather than Maxwell–Wagner type. Both grain and grain boundary resistances were well fitted by the VRH model, suggesting that the VRH mechanism was tenable in both grain and grain boundaries. The electron paramagnetic resonance signal was ascribed to Cu ions, and the linewidth showed a linear relationship with T?1/4, corresponding to the charge transfer between different valence via Cu+-O-Cu2+ and Cu2+-O-Cu3+ paths. The hopping of carriers was also responsible for the conduction and polaron dielectric relaxations.
关键词： Variable-range-hopping conduction,Electron paramagnetic resonance.,Dielectric relaxation,Cu and Nb co-doped BaTiO3
更新于2025-09-23 15:23:52
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heterostructures: Examination of spin relaxation mechanism
摘要： The thickness, temperature, and composition studies of spin diffusion length (SDL) and spin Hall angle (SHA) are performed by measuring the spin Hall magnetoresistance in Pd1?xPtx/Y3Fe5O12 (=YIG) heterostructures. The SDL is found to be invariant to changes in the electron momentum relaxation time by varying the temperature, the normal metal (NM) thickness, or the alloy composition, while the SHA exhibits a nonmonotonic dependence on temperature. These findings suggest the appearance of D’yakonov-Perel’ spin relaxation mechanism and phonon skew scattering in our heterostructures that is associated with strong interfacial Rashba spin-orbit coupling (IRSOC). At last, we employ the ab initio calculations to quantify the IRSOC at the inversion-symmetry-broken NM/YIG interface.
关键词： spin diffusion length,spin relaxation mechanism,spin Hall angle,interfacial Rashba spin-orbit coupling,PdPt/YIG heterostructures
更新于2025-09-23 15:23:52