| 1. |
- Marlton, Frederick P., et al.
(författare)
-
Broad Distribution of Local Polar States Generates Large Electrothermal Properties in Pb-Free Relaxor Ferroelectrics
- 2021
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 33:22
-
Tidskriftsartikel (refereegranskat)abstract
- Electrothermal energy conversion provides attractive solutions for global energy management, such as energy harvesting from waste heat using pyroelectric energy conversion (PEC) and efficient cooling of portable electronics or data servers using the electrocaloric effect. Relaxor ferroelectrics are attractive for electrothermal energy conversion because of their large pyroelectric coefficients over a wide temperature range. Although Pb-based relaxors are well-known, toxicity concerns have mandated the intense search for Pb-free alternatives. Here, we engineered (Ba,Ca)TiO3-based relaxors based on a multisite doping strategy, which show promising electrothermal performance, viz. a maximum PEC efficiency of 14% and electrocaloric refrigeration capacity of 115 J/kg. Using local-scale structural analysis, we provide an atomistic model for large electrothermal properties in the newly designed Pb-free ferroelectrics, whereby a temperature-independent continuous distribution of cation displacement directions creates easy pathways for microscopic polarization reorientation. This research provides key structural insight for future atomic-scale engineering of environmentally sustainable ferroelectrics in energy applications.
|
|
| 2. |
- Nayak, Sanjib, et al.
(författare)
-
Effect of A-site substitutions on energy storage properties of BaTiO 3 -BiScO 3 weakly coupled relaxor ferroelectrics
- 2019
-
Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 102:10, s. 5919-5933
-
Tidskriftsartikel (refereegranskat)abstract
- Weakly coupled relaxors based on compositions (1-x) BaTiO 3 -xBiMeO 3 , where Me is a metal ion, have attracted attention as potential candidates for high-temperature high-energy density capacitors. However, the necessary Bi content is typically high with x = 0.3-0.4. In order to reduce problems associated with compatibility for base metal electrodes and due to additional problems due to Bi volatility, it is desirable to lower the Bi content in the overall composition for these materials. Here, we have explored a possible way to reduce BiMeO 3 content through additional A-site substitutions viz. Ca and Sn. The relaxor nature and energy storage properties of Sn-modified (Ba,Ca)(Ti)O 3 -BiScO 3 ceramics were determined from their dielectric and ferroelectric behaviors. The material showed attractive properties in terms of a frequency-independent (200 Hz-1 MHz) dielectric response from room temperature to 200°C, extremely low loss and high-energy storage efficiency. The structural phenomena underlying the functional properties of Sn-modified (Ba,Ca)TiO 3 -BiScO 3 are characterized from temperature-dependent X-ray diffraction and pair distribution function analysis. In broader terms, the study illustrates the potential for tailoring relaxor behavior in Pb-free ferroelectrics by combining phenomena, such as quantum fluctuations and lone pair stereochemical effect associated with different solid-solution substitutions.
|
|
| 3. |
- Venkateshwarlu, Sarangi, et al.
(författare)
-
Large electromechanical strain and unconventional domain switching near phase convergence in a Pb-free ferroelectric
- 2020
-
Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- In many ferroelectrics, large electromechanical strains are observed near regions of composition- or temperature- driven phase coexistence. Phenomenologically, this is attributed to easy re-orientation of the polarization vector and/or phase transition, although their effects are highly convoluted and difficult to distinguish experimentally. Here, we used synchrotron X-ray scattering and digital image correlation to differentiate between the microscopic mechanisms leading to large electrostrains in an exemplary Pb-free piezoceramic Sn-doped barium calcium zirconate titanate. Large electrostrains of ~0.2% measured at room-temperature are attributed to an unconventional effect, wherein polarization switching is aided by a reversible phase transition near the tetragonal-orthorhombic phase boundary. Additionally, electrostrains of ~0.1% or more could be maintained from room temperature to 140 °C due to a succession of different microscopic mechanisms. In situ X-ray diffraction elucidates that while 90° domain reorientation is pertinent below the Curie temperature (TC), isotropic distortion of polar clusters is the dominant mechanism above TC.
|
|
| 4. |
- Venkateshwarlu, Sarangi, et al.
(författare)
-
Relaxor behavior and electrothermal properties of Sn- And Nb-modified (Ba,Ca)TiO3 Pb-free ferroelectric
- 2020
-
Ingår i: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 35:8, s. 1017-1027
-
Forskningsöversikt (refereegranskat)abstract
- Relaxor ferroelectrics have drawn attention for possible applications in solid-state cooling and thermal energy harvesting, owing to their electrothermal energy conversion properties. Here, we have synthesized and characterized the structure-property correlations of a new Sn- and Nb-doped (Ba,Ca)TiO3 relaxor ferroelectric with large pyroelectric and electrocaloric effects over a broad temperature range. We observed two peaks for the temperature-dependent pyroelectric coefficient: (i) -(δP/δT) ∼ 563 μC/(m2 K) at T ∼ 270 K and (ii) -(δP/δT) ∼ 1021 μC/(m2 K) at T ∼ 320 K. In addition, a broad peak for electrocaloric temperature change is observed near 320 K with a relative cooling power of 1/417 J/kg. These properties could be correlated to structural changes observed using X-ray diffraction at two different temperature ranges in the material. Analysis of high-energy X-ray scattering and specific heat capacity data revealed a transition from the cubic to tetragonal phase near Tm ∼ 320 K, whereas an additional increase in the tetragonality (c/a) of the polar phase is observed below Ts ∼ 270 K.
|
|
