Effects of oxygen isotope and stoichiometry on the structural and transport properties ofLa0.65Ca0.35MnO3−δ

Thermoelectric power (S) and lattice parameter $(a,$ b, $c)$ measurements are used to determine the change in the carrier concentration (n) in both isotope exchanged and oxygen deficient samples of ${\mathrm{La}}_{0.65}{\mathrm{Ca}}_{0.35}{\mathrm{MnO}}_{3-\delta }.$ It is observed upon substitution of the ${}^{18}\mathrm{O}$ isotope for ${}^{16}\mathrm{O}$ that the Curie temperature $T_C$ decreases but no significant changes in S at 290 K and a, b, or c are seen. In contrast, for samples that are oxygen deficient, significant changes in S at 290 K and a, b, and c are observed, in addition to decreases in $T_C.$ It is found that the estimated $\Delta n$ correlating to the observed $\Delta S$ cannot account for the isotope-induced change in $T_C.$ Therefore it is concluded that any oxygen deficiencies introduced by the isotope exchange are negligible and do not account for the $T_C$ change observed.