Optical properties of pyrochlore oxides R<sub>2</sub>Mo<sub>2</sub>O<sub>7- delta </sub> (R: Sm, Gd, and Ho)
N Cao; T Timusk; N P Raju; J E Greedan; P Gougeon; N Cao; Dept. of Phys., McMaster Univ., Hamilton, Ont., Canada; T Timusk; Dept. of Phys., McMaster Univ., Hamilton, Ont., Canada; N P Raju; Dept. of Phys., McMaster Univ., Hamilton, Ont., Canada; J E Greedan; Dept. of Phys., McMaster Univ., Hamilton, Ont., Canada; P Gougeon; Dept. of Phys., McMaster Univ., Hamilton, Ont., Canada
Журнал:
Journal of Physics: Condensed Matter
Дата:
1995-03-20
Аннотация:
The temperature dependence of the reflectance of the spin glass materials R<sub>2</sub>Mo<sub>2</sub>O<sub>7- delta </sub> (R: Sm, Gd, and Ho) has been measured for frequencies from 40 to 40 000 cm<sup>-1</sup> The AC conductivity of Sm<sub>2</sub>Mo<sub>2</sub>O<sub>7- delta </sub> derived from Kramers-Kronig analysis, indicates a Drude-like behaviour as the temperature is lowered. Between 150 and 40 K the scattering rate shows a sharp drop which is attributed to the scattering of conduction electrons by short-range ordered moments of the Mo ions. Below the spin glass transition temperature T<sub>f</sub> ( approximately=40 K) the scattering rate saturates due to the freezing of the moments. Gd<sub>2</sub>Mo<sub>2</sub>O<sub>7- delta </sub> behaves like a poor metal at room temperature, but at low temperatures shows a linear increase in the conductivity for frequencies up to 400 cm<sup>1</sup> suggesting a localized hopping conductivity. The localization remains in the spin glass state for T<T<sub>f</sub> ( approximately=25 K). The conductivity of Ho<sub>2</sub>Mo<sub>2</sub>O<sub>7- delta </sub> is semiconductor-like with a small and slightly temperature-dependent gap around 0.25 eV. Our optical results support a qualitative band model proposed by Sleight and Bouchard for the pyrochlore oxides.
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