Electronic properties of ${\mathrm{Sr}}_{14}$${\mathrm{Cu}}_{24}$${\mathrm{O}}_{41}$

Crystals of orthorhombic ${\mathrm{Sr}}_{14}$ ${\mathrm{Cu}}_{24}$ ${\mathrm{O}}_{41}$ are semiconducting, with an activation energy of 0.18(2) eV for conduction along c, the direction lying parallel to both the (${\mathrm{Cu}}_2$ ${\mathrm{O}}_3$) planes and the (${\mathrm{CuO}}_2$) chains. The magnetic susceptibility above 80 K follows a Curie-Weiss law with θ=-95 K and $p_{\mathrm{eff}}$=0.65${\mu }_B$/Cu in the ac plane and θ=-190 and $p_{\mathrm{eff}}$=0.94${\mu }_B$/Cu along b, the direction perpendicular to the (${\mathrm{Cu}}_2$ ${\mathrm{O}}_3$) planes and the (${\mathrm{CuO}}_2$) chains. There is an indication of antiferromagnetic order below $T_N$=60 K, and a Curie contribution at low temperature due to localized free spins [0.4(1) with S=(1/2 per formula]. The specific heat measured in the range 2–12 K is of the form ${\mathrm{AT}}^{\mathrm{-}2}$+γT+β$T^3$, where A=1080 mJ K/mole, γ=100 mJ/mole ${\mathrm{K}}^2$, and β=5.93 mJ/mole ${\mathrm{K}}^3$. A 5-T magnetic field greatly enhances the low-temperature specific heat, an effect which is attributed to the localized states with S=(1/2. The linear term is attributed to a localized density of states with no net spin, possibly associated with peroxide ions. The relevance of these results to the low-temperature specific heat of copper-oxide superconductors is discussed.