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The intermediate-dimensional hybrid mixed-organic perovskite active layers PEA2(CH3NH3)n−1(PbI2)n and Dodec2(CH3NH3)n−1(PbI2)n with various n values were successfully fabricated. Their characteristics were compared to find out a promising candidate for solar cell applications. The appropriate layer thickness of the films was tuned by a variation of n values based on stoichiometry. The physical appearance, crystal structure, surface morphology, chemical bonding, optical properties, stability to the heat and humidity, and power conversion efficiency of all films were examined thoroughly to determine their potential. For low n values of both film types, they showed the quasi-2D characteristic improving the film stability and conversion efficiency. The absorption edge of both types of materials shifted to a higher energy side and the electronic band gap increased with the decrease of n values. The mixed phase and MAPbI3 perovskite diffraction peaks were still observable even after time has passed for 72 h. Under the 60% humidity condition, the PEA-doped MAPbI3 films decomposed slower than the Dodec-doped MAPbI3 films. [ABSTRACT FROM AUTHOR]

Lead-free (Bi0.46Na0.46Ba0.08)Ti1-xCexO3 (abbreviated as BNBT-xCe, x = 0.01–0.04) ceramics were prepared via conventional solid-state mixed oxide technique. The role of B-site Ce doping was investigated through systematic studies of crystal structure, microstructure, dielectric, ferroelectric and energy-storage properties. All samples exhibited pseudocubic symmetry with an observance of single-phase perovskite structure up to x = 0.02. The SEM micrographs displayed dense microstructure with an average grain size that tended to decrease with increasing Ce doping content. With increasing x, suppression of maximum relative permittivity (εm) and increased broadening of the Tm peak were observed. The change from a square-like ferroelectric to a relaxor-like slim P-E hysteresis loop with a significant drop of Pr was observed at compositions with x ≥ 0.01. Analysis of energy-storage properties revealed the maximum recoverable energy-storage density (Wrec) of 0.28 J/cm3 under applied electric field of 50 kV/cm at x = 0.01. The results demonstrate that Ce modified BNBT ceramics are promising candidate for lead-free energy-storage capacitor applications. [ABSTRACT FROM AUTHOR]

Ceramic systems of Ba1−xLaxTiO3 with La-doping contents of x = 0, 0.005, 0.01, 0.02, 0.04, and 0.08, denoted as BT, BLT0.5, BLT1, BLT2, BLT4, and BLT8, respectively, were synthesized by the solid-state reaction route. All systems were observed the crystal structure, dielectric constant ( ε r ), dielectric loss ( tan ⁡ δ ) , polarization and electric field-induced strain. Thermoelectric properties including electrical resistivity ( ρ), Seebeck coefficient (S), and power factor (PF) of all systems were also performed. The BT0.5 provided the best shot in a term of ferroelectric properties since lanthanum could well diffuse into the BT lattice and enhance the dielectric constant and polarization, while BT1 was quite good for thermoelectric aspect as ion displacement and electrical conductivity was well incorporated. The result suggests that the BT1 system has a possible potential to be further developed for high-temperature thermoelectric applications in the case of polycrystal ceramics. [ABSTRACT FROM AUTHOR]

Phase formations and dielectric properties of lead free barium titanate bismuth zinc zirconate, BaTiO3-Bi(Zn0.5Zr0.5)O3 (BT-BZZ), were comparatively investigated between two different synthesis routes, solid state reaction and salt flux assistance methods. The perovskite (1-x)BT-(x)BZZ ceramics, where x = 0.02, 0.05 and 0.10, were synthesized by using reagent grade oxides and the NaCl salt was used as a surface active agent to lower the calcination temperature. Phase formations were examined by X-ray diffraction technique (XRD). It was found that the solid solutions of (1-x)BT-(x)BZZ can be obtained with lower temperature at least 200 °C via salt flux assistance method. The NaCl salt addition could result in single phase of perovskite structure at every compositions with the calcination temperature as low as 800 °C. Dielectric measurements revealed that the Curie temperature (Tc) shifted to lower temperature with increase of BZZ concentration. Moreover, the dielectric behavior transformed to diffuse phase transition when x = 0.1. The samples prepared via salt flux assistance method exhibited smaller grain size which were revealed by scanning electron microscope. In addition, P-E hysteresis measurements illustrated the higher high E-field dielectric constant with the narrower P-E loop when the salt flux was applied. [ABSTRACT FROM AUTHOR]

The p-type Ca3Co4O9 (CCO) and n-type CaMnO3 (CMO) thermoelectric oxide were synthesized stoichiometrically by the solid-state reaction technique. Both systems were investigated comparatively in aspects of thermoelectric and electrical properties. The material appearance, crystal structure, density, hardness, thermoelectric properties including Seebeck coefficient, electrical resistivity, and thermal conductivity, and electrical properties including dielectric constant, dielectric loss, and complex impedance of both systems were observed. Moreover, the P-E hysteresis loop of ferroelectric property and electrostriction were also investigated. The difference in the crystal structure, phase formation, and crystal growth conducts to the difference in physical, thermoelectric, and electrical properties. CMO was a cubic-perovskite type structure oxide with a higher density, less porosity, and smaller grain size with more thorough distribution as compared to orthorhombic structure CCO. Thus CMO could perform better values in terms of Seebeck coefficient, electrical resistivity, and thermal conductivity. In contrast, CCO possessed a larger grain size with an orthorhombic structure which has more favorable directions for dipole displacement. Hence, CCO exhibited a higher dielectric constant with lower dielectric loss. The complex impedance of both systems was in accordance with the RLC series circuit principle. Unfortunately, the P-E and S-E hysteresis loops of both systems could not be verified due to their electrical conductivity. [ABSTRACT FROM AUTHOR]

B2O3–Bi2O3–SiO2–Sm2O3 glasses have been synthesized by melt quench technique for different mol% Sm2O3. The electrical behavior of these glasses was studied by impedance spectroscopy technique at room temperature, covering the frequency range between 1 M and 1 GHz. In addition, dielectric measurements were made to evaluate the dependence of the dielectric constant different Sm ions. The dielectric constant is approximately 3200 at room temperature for 0.5 mol% Sm-doped compositions at 645 MHz frequency. The results show significant variations for the real part and large variations for the imaginary part among different frequency with different Sm fractions. Complex impedance analysis was used to estimate its electrical conductivity as well as its corresponding optical properties. [ABSTRACT FROM AUTHOR]

Lead-free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3-xNiO (x = 0, 0.2, 0.4, 0.6 and 0.8 wt%) ceramics were prepared by the solid-state combustion technique using glycine as a fuel. The effect of NiO doping on the phase formation, microstructure, electrical and magnetic properties of the ceramics was investigated. The powders and ceramics were calcined and sintered at a temperature of 1050 °C and 1450 °C for 2 h, respectively. XRD results showed that all ceramics had coexisting orthorhombic and tetragonal phases. Increasing the amount of NiO doping enhanced the amount of tetragonal phase, as verified by the Rietveld refinement technique. The density values (ρ) and the average grain size rapidly decreased from 5.79 to 4.69 g/cm3 and 37.8 ± 3.6 to 3.0 ± 0.3 µm when NiO doping increased from 0 to 0.8 wt%. The values of the dielectric constant (ε), dielectric loss (tan δ) and remnant polarization (Pr) tended to decrease when NiO doping increased. Only the sample with 0.4 wt% NiO exhibited ferromagnetic behavior at room temperature, with a remnant magnetization (Mr) and a coercive field (Hc) of 1.04 × 10−5 emu/g and 72.55 Oe, respectively. [ABSTRACT FROM AUTHOR]

In this work, vanadium oxide thin films were prepared by using radio frequency reactive magnetron sputtering with vanadium metal target. The effect of O2 flow rate was investigated in terms of vanadium oxide thin films by varying O2/Ar flow rate at 1/20, 2/20, 3/20, 4/20, 5/20, 6/20 (in sccm unit) with fixed RF power at 200 W and sputtering time at 80 minutes. The surface morphology and crystal structure of V2O5 thin films were investigated by scanning electron microscope (SEM), atomic force microscope (AFM), and X-Ray Diffractometer (XRD) respectively. The influence of the O2/Ar ratio on a local structure of vanadium oxide thin films was studied by the Synchrotron x-ray absorption spectroscopy (XAS) technique. The oxidation states of vanadium oxide thin films were measured at V K-edge by the x-ray absorption near-edge structure (XANES). The results of XANES spectra at the V K-edge showed that the prepared films under the O2/Ar flow rate at 1/20 sccm contained the vanadium with the oxidation states of V3+ and V5+ while the others contained only V5+. This is because the higher O2/Ar flow rate possibly causes an increase in energy flux at the substrate and the 1s→3d transition peak's intensity, which could lead to a higher deposition rate. To achieve the desired V2O5 structure, the gas flow rate could be adjusted properly. The evolution of the local structure around V atoms was studied using the extended x-ray absorption fine structure (EXAFS) which supported the XANES results indicating that the structural environment around V atoms is in good agreement with the V2O5 orthorhombic structure. Finally, XANES and EXAFS fitting results confirmed that the O2 flow rate affected the local structure of vanadium oxide thin films. [ABSTRACT FROM AUTHOR]

This review summarizes the seminal work on the influence of the external stimuli on the dielectric and ferroelectric properties of some technologically important functional materials in the past two decades. These works reflect the important studies of how the external applied electric field and mechanical stress of the properties of materials. In addition to some works by prior important pioneers, the review pointed out several works from our previous investigations on scaling behaviors, in which the effects of field frequency and magnitude were studied in PZT- and BaTiO3-based single crystals and ceramics. The influence of the compressive stress on dielectric and ferroelectric properties of prototypic functional materials was also examined and summarized. In summary, the external stimuli were found to show significant influence on the important properties of these functional materials. [ABSTRACT FROM AUTHOR]

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3-0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area , Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. [ABSTRACT FROM AUTHOR]

In this paper, we report the dielectric and ferroelectric response of compositionally graded bilayer and trilayer composites consisting of BaTiO3 (BT) and 0.975BaTiO3-0.025Ba(Cu1/3Nb2/3)O3 (BTBCN). Two types of graded bilayer samples were synthesized, one with same thickness of BT and BTBCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BTBCN layers of equal thickness. Scanning electron microscopy and transmission electron microscopy images showed a sharp interface with needle-shape domains across the interface. The domain size on BT side was found to be larger than that on BTBCN side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting in characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BTBCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from polarization-electric field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area , Pr, and EC decreased with increasing frequency due to delayed response but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. [ABSTRACT FROM AUTHOR]

This paper proposed an application of Artificial Neural Network (ANN) to concurrently model ferroelectric hysteresis properties of Barium Titanate in both single-crystal and bulk-ceramics forms. In the ANN modeling, there are 3 inputs, which are type of materials (single or bulk), field amplitude and frequency, and 1 output, which is hysteresis area. Appropriate number of hidden layer and hidden node were achieved through a search of up to 2 layers and 30 neurons in each layer. After ANN had been properly trained, a network with highest accuracy was selected. Query file of unseen input data was then input to the selected network to obtain the predicted hysteresis area. From the results, the target and predicted data were found to match very well. This therefore suggests that ANN can be successfully used to concurrently model ferroelectric hysteresis property even though the considered ferroelectrics are with different domains, grains and microscopic crystal structures. [ABSTRACT FROM AUTHOR]

Crystal-structure dependent dynamic scaling behavior was investigated for BaTiO3 ceramic. The scaling relation of the form , (where is the area under the hysteresis loop, while f and E0 represent the frequency and amplitude of the applied electric field signal) was used to determine the values of parameters m and n at various temperatures in the range of −90 °C to 170 °C. The variations in the values of parameters m and n with temperature are explained in terms of the effect of the crystallographic nature of BaTiO3. The values of parameters m and n obtained for the paraelectric regime suggest that the hysteresis in the P–E (polarization–electric field) loops is related to the dielectric loss rather than any domain-related phenomenon. [ABSTRACT FROM AUTHOR]