The photo is sourced from rscf.ru
The classical perovskite (the formula CaTiO3) has a deformed cubic structure and consists of three types of atoms: A (calcium atom), B (titanium atom) and X (three oxygen atoms). The A is located at the centre of pseudocubic structures, the B – at the corner nodes of the pseudocube, and three X atoms form hexagons around the B, with six oxygen atoms around these hexagons. Although the structure is invariant, where A is a large cation (a positively charged ion), B is a smaller cation, and X is an anion (a negatively charged ion), not only calcium and titanium can play the role of the first two atoms but also the minerals with similar properties, such as cerium (a soft, silver-coloured rare earth metal) and niobium (a shiny, silver-gray transition metal).
The structure of the layered perovskites is slightly different: they use four X atoms, and two A atoms, whose role is played by two different minerals. Moreover, in classical perovskites, the octahedrons are interconnected by vertices, and in the layered perovskites, they are connected into layers that are separated by layers with cubic structure of rock salt. This structure provides greater flexibility and more opportunities for improvement.
The research team based on the layered perovskites with the formula BaLaInO4, where the role of the A atoms was played by barium (a soft and viscous silver-white alkaline earth metal) and lanthanum (a shiny rare-earth metal of a silver-white colour), and the role of the B atom was played by indium (brittle and fusible silver-white metal). The scientists added gadolinium atoms to BaLaInO4, which is another rare earth metal with the properties similar to lanthanum. This led to a greater repulsion of octahedrons in a crystal lattice, space expansion for the transfer of the charged particles and, as a result, an increase in the conductivity of materials.
The new modification improved conductivity of the material under dry conditions by about 12 times compared to the original material – this effect was provided mainly by the movement of oxygen ions. The experiment was also conducted in a humid environment, at the temperatures below 400 degrees Celsius, with hydrogen ions as charge carriers: under these conditions, the addition of gadolinium improved conductivity by the factor of 20.
“Our results suggest that the modified layered perovskite can become the basis for hydrogen energy devices. At the moment, we are working on creation of the materials able to effectively combine, in terms of a complex of physicochemical properties, in a solid oxide fuel cell, and we also plan to test them in the future as part of an electrochemical device. This is one of the most important tasks nowadays – making transition from the fundamental materials science to the design of electrochemical devices, so, connecting the fundamental and the applied sciences,” the Russian Science Foundation quotes project leader Natalia Tarasova, Doctor of Chemical Sciences, Professor of Ural Federal University and leading researcher at the Institute of High Temperature Electrochemistry of the Ural Branch of the Russian Academy of Sciences.
