Tel 01223 334496
Email shs28(at)cam.ac.uk
M.Sc. (Physics) Punjab University, Lahore, Pakistan, 1999
M.Sc. (Systems Engineering)Quaid-i-Azam University, Islamabad, Pakistan, 2001
Ferroelectric memory (FRAM) is a leading alternative technology to silicon Flash memory because it is non-volatile, has a rapid erase time and operates at low-voltages. Standard ferroelectric materials for FRAM are (PZT) and (SBT) which are perovskite-type compounds. To further improve their ferroelectric properties additional chemical substitutions have been made resulting in complex solid solutions such as (PZTN), (PLZT) and (BLT). The main materials science issues facing FRAM performance are the microstructure of the perovskite and its interface with an electrode. Both can reduce the switchable polarisation. Charged point defects, in particular, can impede domain wall motion, control switching times, accumulate at the interfaces and influence the Schottky barrier heights. Most DFT calculations in the past have been performed on simple prototypical perovskites such as (BTO) and (PTO). In this project we plan to perform large-scale DFT calculations (>1000 atoms) on the properties of complex perovskite ferroelectrics of commercial importance. Bulk properties will be studied in addition to defects and hetero-interfaces. Of interest are the structure and composition of the bulk, the geometry and electronic properties of defects (eg, oxygen vacancies, grain boundaries, hydrogen impurities), the structure of domain walls and wall-defect interactions, the structure of hetero-interfaces and their interaction with defects, phase transitions and polarisation. ONETEP (Order-N Electronic Total Energy Package) is suitable for dealing with large insulating systems like PZTN, PLZT, SBT and BLT. The electrode-ferroelectric interfaces would need to be handled on a smaller scale using CASTEP. The defining property of ferroelectric materials is the switchable polarization which can be calculated successfully using the modern theory of polarization, i.e., the Berry Phase. It is proposed to implement this theory into ONETEP.