Austrian researchers demonstrated that thin films for condensers may be manufactured not only using expensive vacuum equipment, but also using a much easier and cheaper method – chemical precipitation from a solution. Such films are close to world class samples in terms of their parameters, and even exceeded them in terms of energy absorption capacity when operated in certain modes. We are talking about a very narrow area of material studies, but in essence – about an important step on the way to creating compacted and powerful energy accumulators, which are so much needed in modern electronics.
Condenser is one of the key elements of any appliance: from smartphones and cars to industrial inverters. They are charged and discharged practically instantaneously providing for short, but powerful electric pulses. The problem is that as of now, the amount of energy stored in them is relatively small. We can increase the energy absorption capacity by combining high polarizability of dielectric medium with high electric strength of the material, i.e., the ability to hold off intense fields. But this is a difficult task: the materials with high polarizability usually are bad at holding off the voltage, and the ones that are good at that, usually have very modest polarizability.
Relaxed ferroelectric materials are believed to be the optimal solution. These are the materials with inner nanostructure broken into multiple minor domains. Exposed to the electric field, they can easily switch over, but they almost do not keep high polarizability when they are removed from such field. This decreases the energy losses and improves the efficiency of charging-discharging cycle. Normally, such films are received in vacuum on specialized foundations, which makes their manufacturing more expensive. However, the scientists from the Materials Center Leoben and Silicon Austria Labs succeeded in proving that similar results may be achieved without vacuum units, just by using chemical precursors solution put on usual silicon.
To achieve that, they used lead-free material based on bismuth-sodium titanate (Bi₀.₅Na₀.₅TiO₃) enhanced by magnesium and niobium, which provide структуре prominent relaxed features to the structure. Additional alloying with magnesium decreased the drain currents: magnesium “captures” redundant charges and stabilizes crystal lattice. However, the determinative factor was not just combining the elements, but the thermal treatment mode as well. Quick heating allowed to bypass the temperature ranges, where the deficiencies are usually formed, and lower crystallizing point provided for a dense and even film structure.
Eventually, given the thickness of just 200 nanometers, the film was able to withstand 2.7 MV/cm electric field, which is compatible with the best vacuum technologies. The energy absorbing capacity reached 61 J by cubic cm, and the efficiency – 70%. The films continued to perform in a stable manner when heated up to 160–180 °C, which is critically important for power electronics and hybrid cars. The discharge parameters also proved to be high: the material releases energy for fraction of millisecond, which makes it fit for pulse systems. The durability also turned out high: noticeable change of the properties appeared only after hundreds of thousands of cycles.
This opens up the possibility of inexpensive mass production of ultracompact energy accumulators fit for household electronics, car systems and super-powerful electronic modules.
