Lead-free Ba
0.85
Ca
0.15
Zr
0.10
Ti
0.90
O
3
(BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the morphotropic phase boundary (MPB). Previously, we ...demonstrated that the use of the anionic surfactant sodium dodecyl sulfate (SDS, NaC
12
H
25
SO
4
) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing
1
. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO
3
. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~ 80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164 × 10
−6
K·m/V at 363 K.
The lead-free Ba
0.85
Ca
0.15
Zr
0.10
Ti
0.90
O
3
(BCZT) relaxor ferroelectric ceramic has aroused much attention due to its enhanced piezoelectric, energy storage and electrocaloric properties. In ...this study, the BCZT ceramic was elaborated by the solid-state reaction route, and the temperature-dependence of the structural, electrical, piezoelectric, energy storage and electrocaloric properties was investigated. X-ray diffraction analysis revealed a pure perovskite phase, and the temperature-dependence of Raman spectroscopy, dielectric and ferroelectric measurements revealed the phase transitions in the BCZT ceramic. At room temperature, the strain and the large-signal piezoelectric coefficient
reached a maximum of 0.062% and 234 pm V
−1
, respectively. Furthermore, enhanced recovered energy density (
W
rec
= 62 mJ cm
−3
) and high-energy storage efficiency (
η
) of 72.9% at 130 °C were found. The BCZT ceramic demonstrated excellent thermal stability of the energy storage variation (ESV), less than ±5.5% in the temperature range of 30-100 °C compared to other lead-free ceramics. The electrocaloric response in the BCZT ceramic was explored
via
the indirect approach by using the Maxwell relation. Significant electrocaloric temperature change (Δ
T
) of 0.57 K over a broad temperature span (
T
span
= 70 °C) and enhanced coefficient of performance (COP = 11) were obtained under 25 kV cm
−1
. The obtained results make the BCZT ceramic a suitable eco-friendly material for energy storage and solid-state electrocaloric cooling devices.
High-thermal stability of the recovered energy density and significant electrocaloric temperature change over a broad temperature span in a lead-free BCZT ceramic.
Lead-free Ba
0.85
Ca
0.15
Zr
0.10
Ti
0.90
O
3
(BCZT) ceramics have demonstrated excellent dielectric, ferroelectric, and piezoelectric properties in comparison to lead-based materials. The synthesis ...of pure and crystalline BCZT nanopowders at low temperatures of 25, 80, and 160 °C was reported previously by using a sol–gel method followed by a hydrothermal route. In this study, the structural, dielectric, and ferroelectric properties of sintered BCZT ceramics at 1250 °C/10 h were investigated. XRD measurements revealed the presence of a single perovskite phase at room temperature with the coexistence of the orthorhombic and tetragonal symmetries. The increase of grain size and the ceramic density in BCZT ceramics result in an enhancement of the dielectric and ferroelectric properties of BCZT ceramics. More interestingly, the synthesis temperature of BCZT powders with high dielectric and ferroelectric properties could be decreased to a low temperature of 160 °C, which is about 1200 °C lower when compared with solid-state reaction and 840 °C lower when compared with sol–gel methods. The BCZT ceramics elaborated at 160 °C revealed excellent electrical properties (dielectric constant, dielectric loss, remnant polarization, and maximal polarization of 12,085, 0.017, 8.59 µC/cm
2
, and 27.21 µC/cm
2
, respectively) and enhanced energy performances (recovered energy density and energy efficiency of 367.2 mJ/cm
3
and 67.2%, respectively). Hence, the use of low-temperature hydrothermal processing can be encouraging for the synthesis of lead-free ceramics with high dielectric and ferroelectric properties.
Abstract
Multilevel devices demonstrating switchable polarization enable us to efficiently realize neuromorphic functionalities including synaptic plasticity and neuronal activity. Here we propose ...using the ferroelectric logic unit comprising multiple nanodots disposed between two electrodes and coated by the dielectric material. We devise the integration of the ferroelectric logic unit, providing topologically configurable non-binary logic into a gate stack of the field-effect transistor as an analog-like device with resistive states. By controlling the charge of the gate, we demonstrate the various routes of the topological switchings between different polarization configurations in ferroelectric nanodots. Switching routes between different logic levels are characterized by hysteresis loops with multiple branches realizing specific interconnectivity regimes. The switching between different types of hysteresis loops is achieved by the variation of external fields and temperature. The devised ferroelectric multilevel devices provide a pathway toward the novel topologically-controlled implementation of discrete synaptic states in neuromorphic computing.
A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is ...suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−xPbxTiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.
Lead-free perovskite materials with high performance have high potential in clean energy storage applications and developments of electrocaloric devices. This work reports structural, dielectric, ...ferroelectric, energy storage, and electrocaloric properties near the ambient temperature in barium stannate titanate (BaTi
0.89
Sn
0.11
O
3,
BTS
11
) ceramic prepared by a sol–gel method. A single perovskite structure formation was confirmed using the X-ray diffraction analysis. Average grain size of 18.5 µm was found by the mean of the SEM micrograph with a density of 5.91 g/cm
3
. The multiphase coexistence at very near ambient temperature was proved using temperature-dependent micro-Raman measurements and differential scanning calorimetry. The BTS
11
ceramic exhibits a high dielectric constant of 15,460 and a low dielectric loss (< 0.055) in a broad temperature range. Moreover, a high energy storage density of 122 mJ/cm
3
was shown with an efficiency of 79%, a maximum value of electrocaloric temperature change (Δ
T
) of 0.86 K, and finally, an electrocaloric responsivity (Δ
T
/Δ
E
) of 0.24 K.mm/kV at the external electric field change of 35 kV/cm near ambient temperature. The enhanced dielectric, ferroelectric, and electrocaloric properties make BTS
11
ceramics a great candidate for solid-state cooling technology and high energy storage applications near ambient temperature.
The crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 (x = 0, 0.01, 0.02) solid solutions are studied using X‐ray diffraction (XRD), Raman and terahertz‐infrared (THz‐IR) ...spectroscopies in a temperature range of 4–300 K. XRD and Raman spectroscopy reveal the cubic‐to‐tetragonal nonpolar structural phase transition at about 100 K. At the same time, Raman spectra manifest the presence of polar modes, TO2 and TO4, normally prohibited in paraelectric phase. Emergence of these modes indicates the appearance of the polar nanoregions in a broad temperature range. The modes become more intensive at low temperatures, and temperature dependence of their intensities on cooling reveals the kink‐like change of the slope from flat to steep, indicating on activation of polar nanoregions. The transmission THz‐IR spectra show that squared frequency of the polar TO1 soft mode, responsible for ferroelectric transition, follows Cochran's behavior at high temperatures. However, at low temperatures, it doesn't vanish at extrapolated Curie temperature but saturates, demonstrating the plateau feature below 20 K. This behavior, coherent with known saturation of the dielectric constant, indicates that transition to ferroelectric phase in BaxSr1−xTiO3 is suppressed by quantum fluctuations and the system stays in quantum paraelectric state at very low temperatures.
Crystal structure and lattice dynamics of quantum paraelectric BaxSr1−xTiO3 are studied at temperatures 4–300 K. Polar nanoclusters appear in a broad temperature range and extend with increasing concentration of Ba ions. Clusters’ activation locally stabilizes the ferroelectric phase and reduces the temperature of structural transition. Quantum fluctuations suppress the ferroelectric state, conserving the paraelectric state at very low temperatures.
Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba
0.95
Ca
0.05
Ti
0.89
Sn
0.11
O
3
(BCTSn) elaborated by the sol–gel ...method. Phase purity structure was confirmed from X-ray data using the Rietveld refinement analysis which revealed the coexistence of tetragonal (
P4mm
) and orthorhombic (
Amm2
) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry measurements. The energy storage properties were determined from
P
-
E
hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of Δ
T
= 0.807 K obtained at a relatively small electric field of 30 kV cm
−1
, and the high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications.
Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the ...highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologies.
It is well known that the ferroelectric layers in dielectric/ferroelectric/dielectric heterostructures harbor polarization domains resulting in the negative capacitance crucial for manufacturing ...energy-efficient field-effect transistors. However, the temperature behavior of the characteristic dielectric properties, and, hence, the corresponding behavior of the negative capacitance, are still poorly understood, restraining the technological progress thereof. Here we investigate the temperature-dependent properties of domain structures in the SrTiO
/PbTiO
/SrTiO
heterostructures and demonstrate that the temperature-thickness phase diagram of the system includes the ferroelectric and paraelectric regions, which exhibit different responses to the applied electric field. Using phase-field modeling and analytical calculations we find the temperature dependence of the dielectric constant of ferroelectric layers and identify the regions of the phase diagram wherein the system demonstrates negative capacitance. We further discuss the optimal routes for implementing negative capacitance in energy-efficient ferroelectric field-effect transistors.
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