The dielectric and piezoelectric properties of the ferroelectric BaTiO3 were measured and analyzed using both strong and weak electric field conditions. To measure the electric field induced polarizations and strains, a high voltage source and the measuring circuit were used and the dielectric constants were measured with an impedance analyzer. The spontaneous polarization of BaTiO3 at room temperature was calculated as 17 μC/cm2 based on the lattice structure and internal ion location, which is in good agreement with the experimental results. The polarization and strain hysteresis curve according to the electric field were analyzed in terms of lattice structure and ion position. The magnitude of remanent polarization is proportional to the offset distance of Ti4+ ion from the lattice center. The magnitude of dielectric permittivity is proportional to the degree to which Ti4+ ion can move freely inside the lattice. The magnitude of piezoelectric constant d33 is proportional to how much Ti4+ ion distorts the lattice as it moves inside the lattice.
The increasing demand for renewable energy is driving the rapid expansion of the offshore wind industry, leading to intensified research on subsea cables. These cables endure combined thermal, electrical, and mechanical stresses, with mechanical stress being a critical failure factor. Environmental changes, such as seabed scouring, free spans, and seismic activity, accelerate cable degradation by introducing additional dynamic loads. Conventional monitoring systems primarily track thermal stress, lacking the ability to assess mechanical impacts. This study develops a system to simultaneously measure thermal and mechanical stress in subsea cables. Laboratory experiments confirm the system’s reliability, showing a temperature measurement error within 0.8% at 60℃ and a strain measurement error within 13% at 378 με. The proposed system aims to enhance failure prediction and maintenance strategies for offshore wind subsea cables.
Research on aged insulation of cables by stress is constantly being considered for reliable and stable power transmission of offshore wind farms. This study aimed to evaluate the insulation characteristic of aged XLPE (cross-linked polyethylene) insulation for application of offshore wind farms. In this study, The XLPE insulation of cable was set as various mechanical strains. The XLPE insulation is exposed to the mechanical stress below yield strain of 5%, 10%, and 20%. Aged samples were tested by using the method of AC BDV (alternative current breakdown voltage), tensile strength, elongation, and SEM (scanning electron microscope) to obtain insulation characteristics. The experimental results show that the dielectric breakdown of the sample with a strain 20% was 50% lower than the unaged sample; thereby, demonstrating that the mechanical strain that occurred in the submarine cables can weaken the insulation characteristics. Therefore, mechanical strain should be monitored when laying and operating submarine cables for offshore wind farms.
The measurement of strain under an electric field has been widely employed to comprehend the fundamental principles of electro-mechanical responses in ferroelectric, piezoelectric, and electrostrictive materials. In particular, understanding the strain properties of piezoelectric materials in response to electrical stimulation is crucial for researching and developing components such as piezoelectric actuators, acoustic devices, and ultrasonic generators. This tutorial paper introduces the components and operational principles of the linear variable differential transducer (LVDT), a widely used displacement measurement device in various industries. Additionally, we present the configuration of an experimental setup using LVDT to measure the strain characteristics of ferroelectric, piezoelectric, or electrostrictive materials under the application of an electric field. This paper includes simple measurement results and analyses obtained through the LVDT experimental setup, providing valuable information on research methods for the electro-mechanical interactions of various materials.
In functional materials, in situ experimental techniques as a function of external stimulus (e.g., electric field, magnetic field, light, etc.) or changes in ambient environments (e.g., temperature, humidity, pressure, etc.) are highly essential for analyzing how the physical properties of target materials are activated/evolved by the given stimulation. In particular, in situ electric-field-dependent X-ray diffraction (XRD) measurements have been extensively utilized for understanding the underlying mechanisms of the emerging electromechanical responses to external electric field in various ferroelectric, piezoelectric, and electrostrictive materials. This tutorial article briefly introduces basic principles/key concepts of in situ electric-field-dependent XRD analysis using a lab-scale XRD machine. We anticipate that the in situ XRD method provides a practical tool to systematically identify/monitor a structural modification of various electromechanical materials driven by applying an external electric field.
Al2O3 powders with particle sizes of 0.35 μm, 0.5 μm, 1.5 μm, and 2.5 μm are deposited onto glass and Cu substrates using the aerosol deposition (AD) process. The deposition characteristics of Al2O3 films using those four types of Al2O3 powders are investigated to determine the influence of the particle size on the films. To observe detailed micro-structures of the films, the cross-section and surface morphology are observed. Then, the crystalline size and internal strain are calculated from X-ray diffraction peaks in order to confirm the hammering effect as well as the micro-strain during the AD deposition. From the above results, deposition mechanisms related to the particle size are studied. The results of this study indicate the optimal particle size and formation mechanisms for dense Al2O3 film with a smooth surface roughness as well as for a porous Al2O3 film with a rough surface roughness.
It was proven that the light outputs of blue GaN-based light-emitting diodes (LEDs) was seriously influenced by the application of external stress. We have simulated the wave function overlap of an electron and hole, which are significantly reduced by the development of stress. Consequently, its internal quantum efficiency decreased from 67.0% to 37.5%. To experimentally investigate the effect of stress, we designed and prepared a special zig system. By applying external tensile stress to compensate for the compressive stress innately developed in Blue LEDs, it was found that the optical output was greatly enhanced from 83.1 mcd to 117.2 mcd at a current of 100 mA, an increase of approximately 41%. In contrast, when the compressive stress is developed more by external compressive stress, we observed that the light output power was reduced from 89.0 mcd to 80.7 mcd, a decrease of approximately 9.3%.
The computational fourier-transform moire (CFTM) method has been briefly explained and this method was used to perform strain analysis of a misfit dislocation in a strained Si/Si0.55Ge0.45 layer. An essential advantage of the CFTM method is that it does not require unwrapping, such that errors due to improper unwrapping can be excluded. The analysis results revealed that the Si layer was grown with tensile stress on Si0.55Ge0.45 and lattice constant of the Si layer along the growth direction was 1.9% smaller than that of Si0.55Ge0.45. On the other hand, strain of the misfit dislocation in the strained Si/Si0.55Ge0.45 layer was maximum at the dislocation core due to an extra half-plane and the exx and eyy values were positive and negative, respectively, along the direction of a burgers vector.
The Hall factor in a quantum well structure with X or L-type indirect conduction valleys is calculated for various strain conditions. The two-dimentsional constant energy of occupied valleys are proven to be identical. As a result the Hall factor depends on the direction of occupied valleys to the growth direction, regardless of the number of occupied valleys. This work is widely applicable to the two-dimensional structure with indirect conduction minima for any growth direction and under different strain conditions.
In this paper, semiconducting shield specimens for a DC cable is fabricated and characterized by measurement of volume resistance, tensile strength, and the coefficient of expansion to show the electrical and mechanical characteristics of the semiconducting shield. Due to the PTC phenomenon, the volume resistance at 25℃ increases rapidly in comparison to the volume resistance at 90℃. Since the compounding ratio of carbon black is low, the tensile strength and density become lower and the coefficient of expansion is increased. As the general specification of the tensile strength and density is 0.8 kgf/㎟ and 150%, respectively, the fabricated specimen in this paper has excellent mechanical characteristic.
A highly strained nanostructure comprising crystallographically aligned HgTe nanoinclusions and a surrounding PbTe matrix has been synthesized using a precipitation process of supersaturated HgTe-PbTe alloys. From the early precipitation stage, HgTe nanoinclusions take disk shape, which is transformed from initial HgTe nuclei, although there is no lattice constant difference of the two end components at standard state. As a primary reason for the morphological transformation of the initial spherical HgTe nuclei to HgTe nanodisks, the induced lattice mismatch is suggested. On the condition that the HgTe nanodisks maintain perfect coherent nature with PbTe matrix, the stress-free lattice constant of constrained HgTe nanodisks has been calculated based on the defined concept of the strain-induced tetragonality, the linear elasticity and the actual measurement in HRTEM images.
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