Effects of Three-Dimensional Strain on Electric Conductivity in Au-Dispersed Pr<sub>1.90</sub>Ni<sub>0.71</sub>Cu<sub>0.24</sub>Ga<sub>0.05</sub>O<sub>4+δ</sub>

The effects of tensile strain on the electronic properties of Cu- and Ga-doped Pr<sub>1.9</sub>NiO<sub>4</sub> (PNCG) were investigated. The difference in the thermal expansion coefficient between PNCG (α = 13.5–13.9 × 10<sup>–6</sup> K<sup>–1</sup>) and Au (α = 14.2 × 10<sup>–6</sup> K<sup>–1</sup>) can induce tensile strain in PNCG, resulting in changes in electrical conductivity. Hall-effect measurements indicated that the tensile strain stabilized the oxidized state of PNCG, and the electrical conductivity increased because of the increased hole concentration. This suggests that the tensile strain affected the valence numbers of cations in PNCG, increasing the hole concentration and raising the conductivity. Furthermore, the BO<sub>6</sub> octahedral distance in the K<sub>2</sub>NiF<sub>4</sub> structure was increased by the induced strain, decreasing the hole mobility.