Search

Phase field modeling and computer simulations were conducted to uncover the fundamental mechanism behind the peak in damping capacity observed in BaTiO3-reinforced composites, considering both insulating and conductive cases. The damping capacity curve obtained from these simulations, which varies with temperature, reveals dual peaks near Tc for both cases. The first peak, labeled Peak I, occurs below Tc and is attributed to temperature-induced domain reorientation. The second peak, labeled Peak II, occurs above Tc and arises from stress-induced phase transitions between paraelastic and ferroelastic states. This transition results in a double-loop strain–stress hysteresis, akin to the polarization-field hysteresis observed in ferroelectric systems at and above Tc. Between Peak I and Peak II, there is a dip in damping capacity just below Tc, caused by the diminished ferroelasticity of BaTiO3 particles near this critical temperature. In composite materials, the dual peaks merge into a single peak due to the heterogeneous nature of Tc, influenced by various factors that either raise or lower Tc. This convergence aligns with experimental observations. [ABSTRACT FROM AUTHOR]

The increasing demands of device applications in harsh environments have led to higher expectations for temperature and pressure resistance in high-temperature piezoelectric materials. In order to understand the performance characteristics of BiScO3-PbTiO3 (BS-PT) high-temperature piezoelectric materials in practical device applications, this study focuses on analyzing the dielectric, piezoelectric, and ferroelectric properties of BS-64PT ceramics under uniaxial stress up to 150 MPa, as well as its electromechanical performance under a hydrostatic pressure of up to 400 MPa. As the uniaxial pressure increases, both the bias-field and large-signal piezoelectric coefficients exhibit a pattern of initially increasing and subsequently decreasing. Furthermore, the bias-field piezoelectric coefficient exceeds 450 pC/N and the large-signal piezoelectric coefficient surpasses 630 pC/N under uniaxial pressures below 100 MPa. This highlights their exceptional resistance to depolarization caused by uniaxial stress. To obtain more precise piezoelectric properties for BS-64PT ceramics in the 31 and 33 modes under hydrostatic pressure, the admittance fitting method was utilized. This method takes into account the significant losses at higher pressures. Within the pressure range of 0–400 MPa, the values of d33 and d31 for BS-64PT ceramics exhibited a minor change of 7.6% and 8%, respectively. These findings indicate that BS-64PT ceramics exhibit more stable piezoelectric properties under both uniaxial and hydrostatic pressures when compared to the majority of Pb-based perovskite-structured materials. The exceptional stability of piezoelectric properties in BS-PT ceramics can be primarily attributed to their elevated anisotropy energy or coercivity field compared to other perovskite-structured Pb(Mg1/3Nb2/3)O3 (PMN) / Pb(Zr,Ti)O3 (PZT)-based ceramics reported. [ABSTRACT FROM AUTHOR]

[001]-textured 0.4P(Mg1/3Nb2/3)O3-0.25PbZrO3-0.35PbTiO3-0.5%MnO2 (Mn-PMN-PZT) ceramics were fabricated by templated grain growth using 2 vol. % BaTiO3 in this paper. Full matrices of dielectric (ɛij), elastic (sij, cij), and piezoelectric (dij) parameters were obtained by the resonance–antiresonance method. The dielectric constant ɛ33T of textured ceramics reaches 2600, which is four times that of random ceramics. Textured Mn-PMN-PZT ceramics exhibit high d33 = 984 pC/N and high k33 = 0.89, which is much larger than d33 = 223 pC/N and k33 = 0.70 of random ceramics. However, ɛ11T of ceramics decreases by about 30% after texturing, and the corresponding shear coupling coefficient k15 also decreases from 0.66 to 0.44, which may be due to the reduction in the angle between spontaneous polarization and transverse direction. Furthermore, the temperature stability of the textured ceramics was evaluated as well. The phase transition temperature TR−T was determined by the impedance method to be 120 °C. The textured Mn-PMN-PZT ceramic shows high temperature stability, which is better than PMN-PT. [ABSTRACT FROM AUTHOR]

Electric field-induced antiferroelectric-ferroelectric phase transition and the associated nonlinear dielectric behavior in particulate composites are investigated for achieving a high dielectric capacity. A phenomenological thermodynamic model based on the Landau theory is first developed to discuss the generic phenomena of a temperature-electric field phase diagram, coexistence of antiferroelectric and ferroelectric phases, field-induced antiferroelectric-ferroelectric phase transition, and nonlinear dielectric behavior. The model is then used to carry out the phase field simulation of particulate nonlinear dielectric composites. It is found that the composites exhibit nonlinear dielectric behaviors, and the depolarization field in the composites helps reduce the dielectric hysteresis and enhance the reversibility of antiferroelectric-ferroelectric phase transitions, which are desired for energy storage applications. The simulations also reveal the underlying domain-level mechanisms for nucleation and growth processes of the phase transitions. It is shown that the macroscopic properties of the composites sensitively depend on the directional alignment of the antiferroelectric filler particles, and thus the filler morphology is an effective control variable in designing nonlinear dielectric composites. [ABSTRACT FROM AUTHOR]

360° domain walls in planar magnetic nanowires are studied by micromagnetic simulations. It is shown that a nanowire loop with a shape-isotropic wall generator at one end and a shape-anisotropic wall stopper at the other end functions like a data storage stack: 360° domain walls are generated and pushed into stack under rotating field before overflow while popped out and annihilated when field rotating direction is inverted until underflow. The stack capacity is determined by total nanowire loop length. This simple nanowire structure can be integrated into magnetic circuits as an operation unit for 360° domain wall generation and storage. [ABSTRACT FROM AUTHOR]

To complement recent experimental findings [Vetter et al., APL Mater. 4, 096103 (2016)] on strong exchange coupling effects in Co-Pt nanochessboards featuring a single peak in the first-order reversal curve density plot and associated magnetic hardening as the characteristic structural dimension is reduced below the critical correlation length, the effects of the strong exchange coupling on the underlying magnetic domains and their evolutions are investigated using micromagnetic simulations. The nanochessboard consists of regularly distributed aligned nanorods of a magnetically hard tetragonal L10 phase and a magnetically soft cubic L12 phase, representing a unique type of exchange-coupled magnetic nanocomposites. The simulations reveal detailed magnetic domain processes specific to the nanochessboard structure and uncover an unusual dependence of the coercivity on the length scale, where an expected magnetic hardening is followed by an unexpected magnetic softening with decreasing characteristic dimension. The length scale-dependent exchange coupling effects, effective magnetic anisotropy, and magnetic domain structures and evolution pathways are analyzed to provide insights into the peculiar magnetic behaviors of Co-Pt nanochessboards. [ABSTRACT FROM AUTHOR]