Dielectric,ferroelectric, and piezoelectric properties of lead-free Ba0.95Ca0.05Ti1-xZrxO3 ceramics

Abstract

Ba_0.95Ca_0.05Ti_1-xZr_xO₃ (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'_m), remanent polarization (2P_r), coercive electric field (2E_c) and piezoelectric charge constant (d₃₃) of 7,244, 12.54 (μC/cm²), 5.29 (kV/cm) and 288 (pC/N), respectively.     

Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate and Defect-Healing by I2 Doping

Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short-range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X-ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide-based recipe is found to contain under-coordinated Cu atoms, pointing to the presence of SCN⁻ vacancies. A defect passivation strategy is introduced by adding solid I₂ to the processing solution. At small concentrations, the iodine is found to exist as I⁻ which can substitute for the missing SCN⁻ ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I₂-doped CuSCN as a p-channel in thin-film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I₂ doping method leads to the defect-healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance-voltage characteristics corroborates that the trap state density is reduced upon I₂ addition.     

Design and construction of lightweight EPS geofoam embedded geomaterial embankment system for control of settlements

This paper presents a research study on a bridge site located along US highway 67 over SH 174 in Cleburne, Texas, where bridge approach slabs have experienced more than 0.4 m (17 in.) of settlement within a span of 16 years after construction. Many treatment methods attempted to mitigate this problem had proven to be ineffective. As part of novel rehabilitation works, the top of existing fill soil on the embankment was replaced with lightweight expanded polystyrene (EPS) geofoam blocks to alleviate the approach slab settlements. This paper describes initial design and construction details of the rehabilitation works performed on the embankment system along with a focus on the early performance details. Field monitoring studies were conducted for almost three years to study the bump/settlements under the EPS geofoam embankment system. Short term measured settlement data was analyzed with hyperbolic model to predict the long term settlements. Numerical finite element studies attempted in this study showed that settlements could be reasonably predicted by modeling these geofoam embankments. Based on the monitoring and modeling studies, the effectiveness of utilizing EPS geofoam as an embankment fill material was addressed to mitigate the differential settlements under a bridge approach slab.     

Non‐Ohmic Properties and Electrical Responses of Grains and Grain Boundaries of Na1/2Y1/2Cu3Ti4O12 Ceramics

The dielectric and non‐Ohmic properties of Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramics sintered under various conditions to obtain different microstructures were investigated. Microstructure analysis confirmed the presence of Na, Y, Cu, Ti, and O and these elements were well dispersed in the microstructure. Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramics exhibited non‐Ohmic characteristics with large nonlinear coefficients of about 5.7–6.6 irrespectively of sintering conditions. The breakdown electric field of fine‐grained ceramic with the mean grain size of ≈1.7 μm (≈5600 V/cm) was much larger than those of the course‐grained ceramics with grain sizes of ≈9.5–10.4 μm (≈1850–2180 V/cm). Through optimization of sintering conditions, a low loss tangent of about 0.03 and very high dielectric permittivities of 18 000–23 000 with good temperature stability were successfully accomplished. The electrical responses of the grains and grain boundaries can, respectively, be well described using admittance and impedance spectroscopy analyses based on the brickwork layer model. A possible mechanism for the origin of semiconducting grains is discussed. The colossal dielectric response was reasonably described as closely correlated with the electrically heterogeneous microstructure by means of strong interfacial polarization at the insulating grain‐boundary layers. The non‐Ohmic properties of Na_1/2Y_1/2Cu₃Ti₄O₁₂ ceramics were primarily related to their microstructure, i.e., grain size and volume fraction of grain boundaries.     

Microstructural evolution,non‐Ohmic properties,and giant dielectric response in CaCu3Ti4−xGexO12 ceramics

The microstructural evolution, non‐Ohmic properties, and giant dielectric properties of CaCu₃Ti_4?xGe_xO₁₂ ceramics (x=0‐0.10) are systematically investigated. The Rietveld refinement confirms the existence of a pure CaCu₃Ti₄O₁₂ phase in all samples. Significantly enlarged grain sizes of CaCu₃Ti_4?xGe_xO₁₂ ceramics are associated with the liquid phase sintering mechanism. Enhanced dielectric permittivity from 6.90×10⁴ to 1.08×10⁵ can be achieved by increasing Ge⁴⁺ dopant from x=0‐0.10, whereas the loss tangent is remarkably reduced by a factor of ≈10. Non‐Ohmic properties are enhanced by Ge⁴⁺ doping ions. Using impedance and admittance spectroscopies, the underlying mechanisms for the dielectric and nonlinear properties are well described. The improved nonlinear properties and reduced loss tangent are attributed to the enhanced resistance and conduction activation energy of the grain boundaries. The largely enhanced permittivity is closely associated with the enlarged grain sizes and the increase in the Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ ratios, which are calculated from the X‐ray absorption near‐edge structure.     

Structural study of (1-x)BNKLT-xBZT ceramics using XRD,Raman spectroscopy and XAS

Abstract

The aim of this work is to study the structural phase of (1-x)Bi_0.5(Na_0.74K_0.16Li_0.10)_0.5TiO₃–xBaZr_0.05Ti_0.95O₃ ((1-x)BNKLT-xBZT) ceramics with various x content between 0.025 and 0.150?mol% synthesized via the combustion method. The X-ray diffraction (XRD), Raman spectroscopy and X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), were used to investigate the structural phases of all samples. The XRD pattern and Raman spectra revealed coexisting phases of rhombohedral (R) and tetragonal (T) in all compositions. As the BZT content increased, the phase formation in these samples exhibited higher tetragonality. The quantity of each phase in (1-x)BNKLT-xBZT ceramics can be determined by the XAS technique with Ti K-edge measurements. Increasing the BZT content from 0 to 0.15?mol% caused the R phase to suddenly deceased from 60.9% to 20% while the T phase rapidly increased from 39.1% to 80%. The phase of the structural was determined by several alternative strategies including XRD, Raman and XAS techniques.     

Robust ambiguous target handling for visual object tracking

This paper presents a robust method of handling ambiguous targets (partial occlusion, split region or mixed state of the partial occlusion and the split region) for visual object tracking. The object model is a combination of bounding box features and expected object region. These object properties are very compact and allow us to track objects in a cluttered environment. The target state is classified in the first stage by a state classifier. The state classifier is defined from a weighted cross-correlation of normalized area and normalized distance which are defined from the comparison of background model- and the motion-based object detections. The correlation can categorize the target state by using the overlap quantity of the detected objects from the both object detections. If the target is merged state (partial occlusion), we will identify and track each object in the merged region by the bounding box features. If the targets are the split region, these regions are identified and grouped by the expected object region. If the target is the mixed state, we use the methods for handling the split and the merged region. Finally, experimental results show that the proposed method can deal with tracking in cluttered environments.     

First-principles calculations and experimental study of enhanced nonlinear and dielectric properties of Sn4+-doped CaCu2.95Mg0.05Ti4O12 ceramics

High dielectric permittivity (ε′ ≈ 2000―6900) was accomplished in Sn⁴⁺-doped CaCu_2.95Mg_0.05Ti₄O₁₂ ceramics while retaining a low loss tangent (tanδ ≈ 0.027―0.075). Further, significant improvements in the nonlinear electrical properties, such as high values of the breakdown electric field (E_b ≈ 1.2―1.3 × 10⁴ V cm^?1) and nonlinear coefficient (α ≈ 31), were achieved. In addition, the nonlinear electrical parameters significantly improved, which is consistent with the increase in the electrical resistivities of the grains and grain boundaries due to the decrease in the Cu⁺/Cu²⁺ ratio. According to our first-principles calculations, the Sn atom at the Ti site prefers to be close to the Mg atom at the Cu site, while the oxygen vacancy prefers to be located at large distances from the Sn and Mg co-dopants. This confirms that the dielectric behavior and the nonlinear electrical properties originate from the interface between the grain and grain boundary.