Anisotropic thermoelectric properties associated with dimensional crossover in quasi-one-dimensional SrNbO3.4+d (d ∼ 0.03)

We have grown large single crystals of SrNbO3.4+d (d similar to 0.03) with n = 5 in the homologous series SrnNbnO3n+2 by using a traveling solvent floating-zone method and measured resistivity, thermopower, and thermal conductivity along all crystallographic axes. The thermoelectric properties are found to be highly anisotropic, which reflects a quasi-one-dimensional electronic structure. In particular, the thermopower along the b axis is -170 mu V/K at 300 K, which is 1 order of magnitude higher than the -15 mu V/K along the a axis and -25 mu V/K along the c axis. A possible origin of the high anisotropy in the thermopower is discussed in terms of dimensional crossover associated with a structural modification.