Origin of significantly enhanced dielectric response and nonlinear electrical behavior in Ni2+-doped CaCu3Ti4O12: Influence of DC bias on electrical properties of grain boundary and associated giant dielectric properties

CaCu_3-xNi_xTi₄O₁₂ (x?=?0, 0.05, and 0.10) powders were synthesized using a solid state reaction method. Phase structure and microstructure analyses revealed that all sintered CaCu_3-xNi_xTi₄O₁₂ ceramics were of a pure phase. The CaCu₃Ti₄O₁₂ ceramics had a dense microstructure and grain sizes were enlarged by doping with Ni²⁺. Interestingly, the dielectric permittivity was significantly enhanced, whereas the loss tangent was greatly suppressed to ～0.046–0.034 at 1?kHz. All sintered ceramics exhibited non-Ohmic characteristics. Clarification of the influences of DC bias showed that the dielectric permittivity and loss tangent values were increased by DC bias. The resistance of grain boundaries and the associated conduction activation energy of CaCu_3-xNi_xTi₄O₁₂ ceramics were reduced as the DC bias voltage increased. Therefore, the observed non-Ohmic behavior and significantly enhanced dielectric properties should be closely related to variation in the Schottky barriers at the grain boundaries.     

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.     

Structural and dielectric properties,and nonlinear electrical response of the CaCu3-xZnxTi4O12 ceramics: Experimental and computational studies

CaCu_3-xZn_xTi₄O₁₂ ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu₃Ti₄O₁₂ (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn²⁺ doping ions at Cu²⁺ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu_3-xZn_xTi₄O₁₂ decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu_3-xZn_xTi₄O₁₂ ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn²⁺ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model.     

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.     

Algorithmic Scheme for Concurrent Detection and Classification of Printed Circuit Board Defects

An ideal printed circuit board (PCB) defect inspection system can detect defects and classify PCB defect types. Existing defect inspection technologies can identify defects but fail to classify all PCB defect types. This research thus proposes an algorithmic scheme that can detect and categorize all 14-known PCB defect types. In the proposed algorithmic scheme, fuzzy c-means clustering is used for image segmentation via image subtraction prior to defect detection. Arithmetic and logic operations, the circle hough transform (CHT), morphological reconstruction (MR), and connected component labeling (CCL) are used in defect classification. The algorithmic scheme achieves 100% defect detection and 99.05% defect classification accuracies. The novelty of this research lies in the concurrent use of CHT, MR, and CCL algorithms to accurately detect and classify all 14-known PCB defect types and determine the defect characteristics such as the location, area, and nature of defects. This information is helpful in electronic parts manufacturing for finding the root causes of PCB defects and appropriately adjusting the manufacturing process. Moreover, the algorithmic scheme can be integrated into machine vision to streamline the manufacturing process, improve the PCB quality, and lower the production cost.     

Extremely Enhanced Nonlinear Current–Voltage Properties of Tb‐Doped CaCu3Ti4O12 Ceramics

Nonlinear current–voltage properties of CaCu₃Ti₄O₁₂ ceramics were extremely enhanced by doping with Tb. Substitution of Tb to CaCu₃Ti₄O₁₂ resulted in a decrease in grain size due to the ability of Tb ions to inhibit grain boundary mobility. The dielectric properties of CaCu₃Ti₄O₁₂ ceramics were degraded after doping with Tb. Surprisingly, the nonlinear electrical properties were strongly enhanced. The best properties with a nonlinear coefficient of ~29.67 and breakdown electric field strength of ~1.52 × 10⁴ V/cm were obtained in the Ca_0.775Tb_0.15Cu₃Ti₄O₁₂ ceramic. These extremely enhanced properties were attributed to modification of grain boundary electrical response due to the effect Tb substitution.     

Ge4+ doped CaCu2.95Zn0.05Ti4O12 ceramics: Two-step reduction of loss tangent

CaCu₃Ti₄O₁₂ ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu₃Ti₄O₁₂ with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 10³ to 3.93 × 10⁴ Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu₃Ti₄O₁₂ ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge⁴⁺ dopant into the Zn²⁺-doped CaCu₃Ti₄O₁₂ ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 10⁵ Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 10⁴). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu₃Ti₄O₁₂ structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors.     

Enhance Egocentric Grasp Recognition Based Flex Sensor Under Low Illumination

Egocentric recognition is exciting computer vision research by acquiring images and video from the first-person overview. However, an image becomes noisy and dark under low illumination conditions, making subsequent hand detection tasks difficult. Thus, image enhancement is necessary to make buried detail more visible. This article addresses the challenge of egocentric hand grasp recognition in low light conditions by utilizing the flex sensor and image enhancement algorithm based on adaptive gamma correction with weighting distribution. Initially, a flex sensor is installed to the thumb for object manipulation. The thumb placement that holds in a different position on the object of each grasp affects the voltage changing of the flex sensor circuit. The average voltages are used to configure the weighting parameter to improve images in the image enhancement stage. Moreover, the contrast and gamma function are used to adjust varies the low light condition. These grasp images are then separated to be training and testing with pre-trained deep neural networks as the feature extractor in YOLOv2 detection network for the grasp recognition system. The proposed of using a flex sensor significantly improves the grasp recognition rate in low light conditions.     

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.