The anomalous phase transition of zinc ferrite nanocrystals under pressure

The electric resistance and capacitance of different sized free-standing ZnFe2O4 nanocrystals were measured under pressure up to 20 GPa in a diamond anvil cell at ambient temperature. The experimental results demonstrate that phase transition takes place at 5.5 GPa and 8.9 GPa for 5 nm and 70 nm nanocrystals, respectively, in contrast to the prediction of scaling theory on the phase transformation of semiconductor nanocrystals. When the pressure exceeds the phase transition pressure, the resistance and capacitance of ZnFe2O4 nanocrystals decrease exponentially with pressure following the relationships R similar to exp(-CRP) and C similar to exp(-CCP), where C-R = 0.4739 GPa(-1) and C-C = 0.5263 GPa(-1) for 5nm ZnFe2O4 crystals, CR = 0.1667 GPa(-1) and C-C = 0.2447 for the 70 nm one. It is interesting that the pressure-dependent resistance profile changed significantly when the samples were treated with minor water before pressing. The nanocrystals follow the rule that small particle grows and largo particle decreases under pressure.