This review covers recently reported polymer composites that show a thermoelectric (TE) effect and thus have potential application as thermoelectric generators and Peltier coolers. The growing need ...for CO2‐minimizing energy sources and thermal management systems makes the development of new TE materials a key challenge for researchers across many fields, particularly in light of the scarcity or toxicity of traditional inorganic TE materials based on Te and Pb. Recent reports of composites with inorganic and organic additives in conjugated and insulating polymer matrices are covered, as well as the techniques needed to fully characterize their TE properties.
Energy budget: This Minireview summarizes recently reported polymer composites that show a thermoelectric (TE) effect and thus have potential application as thermoelectric generators and Peltier coolers. Composites with inorganic and organic additives in conjugated and insulating polymer matrices are covered, as well as the techniques needed to characterize their TE properties.
Experimental search for high-temperature ferroelectric perovskites is a challenging task due to the vast chemical space and lack of predictive guidelines. Here, we demonstrate a two-step machine ...learning approach to guide experiments in search of xBiFormula: see textO
-(1 - x)PbTiO
-based perovskites with high ferroelectric Curie temperature. These involve classification learning to screen for compositions in the perovskite structures, and regression coupled to active learning to identify promising perovskites for synthesis and feedback. The problem is challenging because the search space is vast, spanning ~61,500 compositions and only 167 are experimentally studied. Furthermore, not every composition can be synthesized in the perovskite phase. In this work, we predict x, y, Me', and Me″ such that the resulting compositions have both high Curie temperature and form in the perovskite structure. Outcomes from both successful and failed experiments then iteratively refine the machine learning models via an active learning loop. Our approach finds six perovskites out of ten compositions synthesized, including three previously unexplored {Me'Me″} pairs, with 0.2Bi(Fe
Co
)O
-0.8PbTiO
showing the highest measured Curie temperature of 898 K among them.
Charge-transport and electrochemical processes are heavily influenced by the local microstructure. Kelvin probe force microscopy (KPFM) is a widely used technique to map electrochemical potentials at ...the nanometer scale; however, it offers little information on local charge dynamics. Here, we implement a hyperspectral KPFM approach for spatially mapping bias-dependent charge dynamics in timescales ranging from the sub-millisecond to the second regime. As a proof of principle, we investigate the role mobile surface charges play in a three-unit-cell LaAlO3/SrTiO3 oxide heterostructure. We explore machine learning approaches to assist with visualization, pattern recognition, and interpretation of the information-rich data sets. Linear unmixing methods reveal hidden bias-dependent interfacial processes, most likely water splitting, which are essentially unnoticed by functional fitting of the dynamic response alone. Hyperspectral KPFM will be beneficial for investigating nanoscale charge transport and local reactivity in systems involving a possible combination of electronic, ionic, and electrochemical phenomena.
Abstract
Unraveling local dynamic charge processes is vital for progress in diverse fields, from microelectronics to energy storage. This relies on the ability to map charge carrier motion across ...multiple length- and timescales and understanding how these processes interact with the inherent material heterogeneities. Towards addressing this challenge, we introduce high-speed sparse scanning Kelvin probe force microscopy, which combines sparse scanning and image reconstruction. This approach is shown to enable sub-second imaging (>3 frames per second) of nanoscale charge dynamics, representing several orders of magnitude improvement over traditional Kelvin probe force microscopy imaging rates. Bridging this improved spatiotemporal resolution with macroscale device measurements, we successfully visualize electrochemically mediated diffusion of mobile surface ions on a LaAlO
3
/SrTiO
3
planar device. Such processes are known to impact band-alignment and charge-transfer dynamics at these heterointerfaces. Furthermore, we monitor the diffusion of oxygen vacancies at the single grain level in polycrystalline TiO
2
. Through temperature-dependent measurements, we identify a charge diffusion activation energy of 0.18 eV, in good agreement with previously reported values and confirmed by DFT calculations. Together, these findings highlight the effectiveness and versatility of our method in understanding ionic charge carrier motion in microelectronics or nanoscale material systems.
Compositional modification of ferroelectric BiScO3–PbTiO3 (BS–PT) ceramics was investigated by ZrSc• doping as a function of temperature and electric field. Zr doping decreased the Curie temperature; ...yet depoling temperature was higher as determined from the weak field measurements. Weight change measurements explain the difference in sintering behavior, emphasizing the effects of sacrificial powder on the defect structure. Possible mechanisms are discussed in collaboration with the crystal structure analysis. Pb′Bi replacement was shown as a possible charge balance mechanism. Pb′Bi is supported by the weight loss data, crystal structure analysis and the weak‐field electrical and electromechanical measurements. However, high field measurements contradicted the postulated Pb′Bi mechanism. Unipolar and bipolar high field polarization, strain and dielectric constant measurements indicated that the donor doping creates A‐site vacancies; a similar observation to Pb(Zr,Ti)O3 (PZT)‐based ceramics. At higher temperatures, the property dependence on the composition decreased suggesting that thermally assisted domain motion eliminated the dependence of the domain wall mobility on the extrinsic contributions (i.e., defect structure induced by doping). Effect of ZrSc• doping on electrical and electromechanical properties are reported and discussed as a function of temperature.
2.5Bi(Zn
0.5
Zr
0.5
)O
3
−37.5BiScO
3
−60PbTiO
3
(BZZ-BS-PT) ceramics were successfully textured in the 001 by templated grain growth (TGG) process using 5 vol% -oriented BaTiO
3
(BT) plate-like ...templates. The templates were aligned in the matrix powder via tape casting and textured BZZ-BS-PT ceramics sintered at 1100°C for 3 h in air had a relative density of 98% and a Lotgering factor of 0.91. Chemically stable BT templates in Pb and Bi-rich BZZ-BS-PT system gave rise to the formation of highly oriented polycrystalline structure with larger block-like grains. A very high unipolar strain of 0.3% and low-field (<5 kV/cm) piezoelectric charge coefficient (d
33
) of 930 pm/V when driven at 50 kV/cm were achieved in highly textured ceramics together with a Curie temperature (T
C
) of 403°C. The TGG approach significantly improved piezoelectric properties of the BZ-BS-PT ceramic system without deteriorating the dielectric properties, which is a very promising high-performance candidate for high-temperature sensor, transducer and actuator applications.
The 26th International Symposium on the Applications of Ferroelectrics (ISAF) was held jointly with the International Workshop on Acoustic Transduction Materials and Devices (IWATMD) and ...Piezoresponse Force Microscopy Workshop (PFM), on May 7-11, 2017, at the Georgia Institute of Technology, Atlanta, GA, USA.
Ternary phase diagram of BiScO3 (BS), PbZrO3 (PZ), and PbTiO3 (PT) was explored for identification of high‐performance piezoelectrics for actuator applications. The ternary morphotropic phase ...boundary (MPB) connecting the binary MPBs of BS–PT (45/65) and PZ–PT (52/48) was determined using X‐ray diffraction (XRD). High‐temperature XRD and dielectric measurements were used to determine the phase transformation temperatures. Curie temperature (TC) had a near linear dependence on composition, rate of which is determined for each component of the ternary independently. Specimens on the tetragonal side of the MPB exhibited lower high field resistivity and proper poling was not possible. Specimens on the rhombohedral side were superior with saturated hysteresis loops and piezoelectric coefficient (d33)>400 pm/V. Unlike phase transformation temperatures, the proximity to MPB was more dominant than the compositional effects in determining electrical and electromechanical properties, which maximized for the compositions closest to the MPB. Both weak‐ and high field properties are reported as a function of temperature.
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