Acting like thermal resistances, ferroelectric domain walls can be manipulated to realize dynamic modulation of thermal conductivity (
Domain features and domain walls in lead halide perovskites (LHPs) have attracted broad interest due to their potential impact on optoelectronic properties of this unique class of solution‐processable semiconductors. Using
- NSF-PAR ID:
- 10386739
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 35
- Issue:
- 8
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract k ), which is essential for developing novel phononic circuits. Despite the interest, little attention has been paid to achieving room‐temperature thermal modulation in bulk materials due to challenges in obtaining a high thermal conductivity switching ratio (k high/k low), particularly in commercially viable materials. Here, room‐temperature thermal modulation in 2.5 mm‐thick Pb(Mg1/3Nb2/3)O3–x PbTiO3(PMN–x PT) single crystals is demonstrated. With the use of advanced poling conditions, assisted by the systematic study on composition and orientation dependence of PMN–x PT, a range of thermal conductivity switching ratios with a maximum of ≈1.27 is observed. Simultaneous measurements of piezoelectric coefficient (d 33) to characterize the poling state, domain wall density using polarized light microscopy (PLM), and birefringence change using quantitative PLM reveal that compared to the unpoled state, the domain wall density at intermediate poling states (0<d 33<d 33,max) is lower due to the enlargement in domain size. At optimized poling conditions (d 33,max), the domain sizes show increased inhomogeneity that leads to enhancement in the domain wall density. This work highlights the potential of commercially available PMN–x PT single crystals among other relaxor‐ferroelectrics for achieving temperature control in solid‐state devices. -
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Abstract Halide perovskites are revolutionizing the renewable energy sector owing to their high photovoltaic efficiency, low manufacturing cost, and flexibility. Their remarkable mobility and long carrier lifetime are also valuable for information technology, but fundamental challenges like poor stability under an electric field prevent realistic applications of halide perovskites in electronics. Here, it is discovered that valleytronics is a promising route to leverage the advantages of halide perovskites and derivatives for information storage and processing. The synthesized all‐inorganic lead‐free perovskite derivative, Cs3Bi2I9, exhibits strong light–matter interaction and parity‐dependent optically addressable valley degree of freedom. Robust optical helicity in all odd‐layer‐number crystals with inversion symmetry breaking is observed, indicating excitonic coherence extending well beyond 11 layers. The excellent optical and valley properties of Cs3Bi2I9arise from the unique parallel bands, according to first principles calculations. This discovery points to new materials design principles for scalable valleytronic devices and demonstrates the promise of perovskite derivatives beyond energy applications.
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Abstract Domain walls separating regions of ferroelectric material with polarization oriented in different directions are crucial for applications of ferroelectrics. Rational design of ferroelectric materials requires the development of a theory describing how compositional and environmental changes affect domain walls. To model domain wall systems, a discrete microscopic Landau–Ginzburg–Devonshire (dmLGD) approach with A‐ and B‐site cation displacements serving as order parameters is developed. Application of dmLGD to the classic BaTiO3, KNbO3,and PbTiO3ferroelectrics shows that A–B cation repulsion is the key interaction that couples the polarization in neighboring unit cells of the material. dmLGD decomposition of the total energy of the system into the contributions of the individual cations and their interactions enables the prediction of different properties for a wide range of ferroelectric perovskites based on the results obtained for BaTiO3, KNbO3,and PbTiO3only. It is found that the information necessary to estimate the structure and energy of domain‐wall “defects” can be extracted from single‐domain 5‐atom first‐principles calculations, and that “defect‐like” domain walls offer a simple model system that sheds light on the relative stabilities of the ferroelectric, antiferroelectric, and paraelectric bulk phases. The dmLGD approach provides a general theoretical framework for understanding and designing ferroelectric perovskite oxides.
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Domain walls’ vibration and motion contribute significantly to the exceptionally large dielectric and piezoelectric response of ferroelectric materials. Yet, the specific length scales at which domain walls impact characteristic parameters remain largely unprobed. Previous studies examining correlation of domain wall proximity and functional response at the micrometer or submicrometer scales are often based on (locally or globally) “written” domains. The stability of such domains can be affected by many factors, resulting in convoluted effects of domain wall proximity and their stability when studying the local functional response. Herein, the effects of preexisting domain walls on the nanoscale polarization switching in a [001]‐cut relaxor‐ferroelectric single crystal are probed by piezoresponse force microscopy. It is found that domain wall proximity has limited impact on polarization switching for locations ⪝300 nm away. While a transition from a growth‐ to nucleation‐limited regime and/or change in dimensionality of domain growth is possibly observed, the effective impact on nucleation voltage does not exceed 25% variation. These results are consistent with the well‐documented pervasive chemical, polar, and structural heterogeneities present in relaxor‐ ferroelectrics and the resulting “soft” piezoelectric behavior.
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