Examples include ferroelectrics, which show a spontaneous electric polarisation (analogous to ferromagnetism), ferroelastics (which show spontaneous strain) or materials – multiferroics – which show a combination of magnetic, electric or elastic behaviour. Of importance for the properties and behaviour of such materials is the size of the strain field around individual dopant atoms. One method of measuring this is to determine the extent to which a material’s transition temperature remains independent of dopant concentration for a suitable phase transition. In principle the transition temperature will not change from that of the pure phase until the strain fields around individual impurity atoms start to overlap. We have used HRPD to make precise measurements of the monoclinic to orthorhombic transition occurring in La-doped PrAlO3 at about 150 K. We find this temperature is unchanged to a La dopant level of about 1.6%, and infer strain fields of order 1.6-1.8 pm diameter. This appears to be a characteristic length scale for strain relaxation around impurities in oxide perovskites.
MA Carpenter, CJ Howard (Cambridge University), BJ Kennedy, Q Zhou (Sydney University), KS Knight (ISIS)
Research date: September 2009
Contact: Prof MA Carpenter, firstname.lastname@example.org
Further reading: MA Carpenter et al., to appear in Phys Rev B (2009)