Effects of pressure on electron transport and atomic structure of manganites: Low to high pressure regimes

The pressure dependence of the resistivity and structure of (formula presented) has been explored in the pressure range from 1 atm to ∼7 GPa. The metal to insulator transition temperature (formula presented) was found to reach a maximum and the resistivity achieves a minimum at ∼3.8 GPa. Beyond this pressure, (formula presented) is reduced with a concomitant increase in the resistivity. Structural measurements at room temperature show that at low pressure (below 2 GPa) the Mn-O bond lengths are compressed. Between ∼2 and ∼4 GPa, a pressure-induced enhancement of the Jahn-Teller (JT) distortion occurs in parallel with an increase in Mn-O1-Mn bond angle to ∼180°. Above ∼4 GPa, the Mn-O1-Mn bond angle is reduced, while the JT distortion appears to remain unchanged. The resistivity above (formula presented) is well modeled by variable range hopping. The pressure dependence of the localization length follows the behavior of (formula presented).