Scientists find how Charge-Carrying Particles move in Perovskite
Perovskites can be used in solar batteries of future. New results will help scientists to search for a required perovskite structure by taking into account its fundamental features, rather than at random. Perovskite is a material with an almost ideal structure. The majority of high-temperature superconductors are perovskite-based due to their non-ideal structure. The material can also be used to produce flexible solar batteries without rare-earth metals, which would help to reduce costs and enable large-scale manufacture.
“This material exhibits many interesting and intriguing properties, most notably giant magnetoresistance. Many manganite properties are unknown, despite the fact that manganites have been studied for decades. We tried to work out what the conduction mechanism is of one of the most common compounds – Pr1-xCaxMnO3,” he says. All these features have been experimentally discovered, but the processes to explain these unique properties are unknown.
To test which particles are conductive, they applied different frequency voltages and measured the relationship between frequency and induced current. The scientists measured the frequency and temperature dependence of conductivity and permittivity in a broad frequency range (5-3000 cm-1) to cover all the bases. Wide temperature ranges – from 10 to 300 K of the samples were obtained to distinguish similar dependences of samples with different conduction mechanisms. But even this was insufficient to clarify the nature of charge carries. For this reason, researchers compared perovskites with different ratios of calcium (Ca) and praseodymium (Pr).
The group of scientists discovered that the charge carriers in Pr1-xCaxMnO3 perovskites are polarons (electrons moving through atoms of a material, causing the neighboring positive charges to shift toward it and the neighboring negative charges to shift away). The properties of perovskites are ideal for electron-phonon (phonons are vibrations in a crystal lattice) coupling, determined by the interplay between symmetry breaking interactions. The researchers established that polarons move coherently (as one unit) ie charge carriers behave more like uncoupled particles. The idea of coherence is used in lasers, superconductors, highly accurate distance measurements, quantum calculations etc.
Establishing how conduction occurs could help perovskite research projects and large-scale applications to progress. Eg there is already a high-efficiency perovskite-based device for separating water into oxygen and hydrogen. Perovskites can also be used as LEDs, however they are currently only able to function at the temperature of liquid nitrogen. https://mipt.ru/english/news/scientists_explain_unusual_and_effective_features_in_perovskite
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