“The phase transitions below 105 Kelvin stretch the crystal structure, creating dipoles. We show that oxygen vacancies accumulate at the domain walls and that these walls offer the channel for the movement of oxygen vacancies. These channels are responsible for memristive behaviour in STO,” said Banerjee. Accumulation of oxygen vacancy channels in the crystal structure of STO explains the shift in the position of the minimum conductivity.
Chen also carried out another experiment: “We kept the STO gate voltage at -80 V and measured the resistance in the graphene for almost half an hour. In this period, we observed a change in resistance, indicating a shift from hole to electron conductivity.,” she said. This effect is primarily caused by the accumulation of oxygen vacancies at the STO surface.
The experiments show that the properties of the combined STO/graphene material change through the movement of both electrons and ions, each at different time scales. “By harvesting one or the other, we can use the different response times to create memristive effects, which can be compared to short-term or long-term memory effects,” said Bannerjee.
The study creates new insights into the behaviour of STO memristors. “And the combination with graphene opens up a new path to memristive heterostructures combining ferroelectric materials and 2D materials,” she added.
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