Amorphous Piezo‐ and Pyroelectric Phases of BaZrO<sub>3</sub> and SrTiO<sub>3</sub>

Ehre, David; Lyahovitskaya, Vera; Tagantsev, A. K.; Lubomirsky, Igor

doi:10.1002/adma.200602149

Cited by 46 publications

(48 citation statements)

References 16 publications

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“…As in our earlier work on MAPbBr 3 (22), we used periodic pulse pyroelectric measurements (45)(46)(47) to determine whether tetragonal MAPbI 3 is polar along its c axis. Pyroelectric currents can be distinguished from other possible thermally stimulated electric response (TSER) (thermoelectricity or flexoelectricity) (22,48) by heating once one, and once the other side of the crystal periodically.…”

Section: Resultsmentioning

confidence: 99%

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Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Rakita

Bar-Elli

Meirzadeh

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

264

221

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Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI 3 ). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI 3 is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI 3 (unlike MAPbBr 3 ) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material's relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity's hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI 3 , we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material's noncentrosymmetry. We note that the material's ferroelectric nature, can, but need not be important in a PV cell at room temperature.halide perovskites | photovoltaics | semiconductors | ferroelectricity | pyroelectricity N ew optoelectronic materials are of interest for producing solar cells with higher power and voltage efficiencies, lower costs, and improved long-term reliability. A very recent entry is the family of halide perovskites (HaPs), in particular those based on methylammonium (MA) lead iodide (MAPbI 3 ), MAPbBr 3 , and its inorganic analog CsPbBr 3 . Devices based on these perform remarkably well as solar cells (1, 2), as well as in other optoelectronic applications, such as LEDs and electromagnetic radiation detectors (3-5). Understanding possible unique characteristics of HaPs may show the way to other materials with similar key features.The ABX 3 (X = I, Br, Cl) HaP semiconductors (SCs), that is, with perovskite or perovskite-like structures, reach, via a steep absorption edge, a high optical absorption coefficient (∼10 5 cm −1 ) (6, 7), long charge carrier lifetimes (∼0.1-1 μs) (8), and reasonable carrier mobilities (less than or equal to ∼100 cm 2 ·V −1 ·s −1 ) (9), and have a low exciton binding energy (10). With these characteristics, the thickness of the optical absorber layer can be ≤0.5 μm, which allows the charge carriers (separated electrons and holes) to diffuse/d...

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Section: Resultsmentioning

confidence: 99%

“…A periodic temperature change (Chynoweth) method, was used to measure pyroelectricity (45)(46)(47). A general scheme of the setup (heat generation and pyroelectric current measurement) is visualized in Fig.…”

Section: Methodsmentioning

confidence: 99%

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Rakita

Bar-Elli

Meirzadeh

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

264

221

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“…Recently, Lubomirsky and coworkers [75,[94][95][96] presented experimental data on perovskite thin films, which strongly suggest that a strain gradient can pole an amorphous material when it is thermally treated in a special way. It was shown that during such treatment the material is passing between two different amorphous states.…”

Section: Plastic Flexoelectricitymentioning

confidence: 99%

Fundamentals of flexoelectricity in solids

2013

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The flexoelectric effect is the response of electric polarization to a mechanical strain gradient. It can be viewed as a higher-order effect with respect to piezoelectricity, which is the response of polarization to strain itself. However, at the nanoscale, where large strain gradients are expected, the flexoelectric effect becomes appreciable. Besides, in contrast to the piezoelectric effect, flexoelectricity is allowed by symmetry in any material. Due to these qualities flexoelectricity has attracted growing interest during the past decade. Presently, its role in the physics of dielectrics and semiconductors is widely recognized and the effect is viewed as promising for practical applications. On the other hand, the available theoretical and experimental results are rather contradictory, attesting to a limited understanding in the field. This review paper presents a critical analysis of the current knowledge on the flexoelectricity in common solids, excluding organic materials and liquid crystals.

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“…The anisotropy of the refractive index and the development of in-plane compressive stress may serve as unambiguous indicators of the transformation into the quasi-amorphous phase. In contrast to the refractive index, which decreases during the transformation of the amorphous into the quasi-amorphous phase, the dielectric constant increases during this transformation by 15-40% but remains far smaller than the dielectric constant of the corresponding crystalline phases ($22 and $33 for quasi-amorphous SrTiO 3 and BaTiO 3 , respectively [5,10] ). Monitoring changes in refractive indices, in-plane stress, and dielectric constant can be an efficient tool for tailoring film preparation conditions.…”

Section: Preparation and Physical Properties Of Quasi-amorphous Thin mentioning

confidence: 86%

“…[5] Subsequent investigation of this phase, called quasi-amorphous, [6][7][8][9] confirmed the conclusion that compounds that do not form polar crystalline polymorphs may nevertheless form polar quasi-amorphous phases that exhibit pyro-and piezoelectricity. [10] This hypothesis was later confirmed by the observation of the quasi-amorphous phase in SrTiO 3 and BaZrO 3 films. Data from extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray photoelectron spectroscopy (XPS) led to the development of a theory that describes the formation and microscopic origin of polarity in quasi-amorphous films.…”

Section: Introductionmentioning

confidence: 85%

Quasi‐Amorphous Inorganic Thin Films: Non‐Crystalline Polar Phases

Wachtel

Lubomirsky

2010

Advanced Materials

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Quasi-amorphous thin films of BaTiO3, SrTiO3, and BaZrO3 are the only known examples of inorganic, non-crystalline, polar materials. The conditions under which they are formed and the origin of their polarity set these materials apart from other classes of inorganic materials. The most important feature of the quasi-amorphous phase is that the polarity is the result of the orientational ordering of local bonding units but without any detectable spatial periodicity. This mechanism is reminiscent of that observed in ferroelectric polymers and permits compounds that do not have polar crystalline polymorphs, such as SrTiO3 and BaZrO3, to form polar non-crystalline solids. In the present report, we provide an overview of the essential features of these materials including preparation, structure, and chemical composition. The report also reviews our current level of understanding and offers some guidelines for further development and application of non-crystalline inorganic polar materials.

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Amorphous Piezo‐ and Pyroelectric Phases of BaZrO₃ and SrTiO₃

Cited by 46 publications

References 16 publications

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Fundamentals of flexoelectricity in solids

Quasi‐Amorphous Inorganic Thin Films: Non‐Crystalline Polar Phases

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Amorphous Piezo‐ and Pyroelectric Phases of BaZrO3 and SrTiO3

Cited by 46 publications

References 16 publications

Tetragonal CH 3 NH 3 PbI 3 is ferroelectric

Tetragonal CH 3 NH 3 PbI 3 is ferroelectric

Fundamentals of flexoelectricity in solids

Quasi‐Amorphous Inorganic Thin Films: Non‐Crystalline Polar Phases

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Amorphous Piezo‐ and Pyroelectric Phases of BaZrO₃ and SrTiO₃

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric