Thermopower and electrical resistivity measurements transverse to the conducting chains of the quasi-one-dimensional metal Li(0.9)Mo(6)O(17) are reported in the temperature range 5 K <= T <= 500 K. For T>= 400 K the interchain transport is determined
by thermal excitation of charge carriers from a valence band ~ 0.14 eV below the Fermi level, giving rise to a large, p-type thermopower that coincides with a small, n-type thermopower along the chains. This dichotomy -- semiconductor-like in one direction and metallic in a mutually perpendicular direction -- gives rise to substantial transverse thermoelectric (TE) effects and a transverse TE figure of merit among the largest known for a single compound.
A correlation between lattice parameters, oxygen composition, and the thermoelectric and Hall coefficients is presented for single-crystal Li(0.9)Mo(6)O(17), a quasi-one-dimensional (Q1D) metallic compound. The possibility that this compound is a com
pensated metal is discussed in light of a substantial variability observed in the literature for these transport coefficients.
The Nernst coefficient for the quasi-one-dimensional metal, Li(0.9)Mo(6)O(17), is found to be among the largest known for metals (~500 microV/KT at T~20K), and is enhanced in a broad range of temperature by orders of magnitude over the value expected
from Boltzmann theory for carrier diffusion. A comparatively small Seebeck coefficient implies that Li(0.9)Mo(6)O(17) is bipolar with large, partial Seebeck coefficients of opposite sign. A very large thermomagnetic figure of merit, ZT~0.5, is found at high field in the range T~35-50K.
The structure, morphology, and electrical properties of epitaxial a-axis oriented thin films of Nd(0.2)Sr(0.8)MnO(3) are reported for thicknesses 10 nm <= t <= 150 nm. Films were grown with both tensile and compressive strain on various substrates. I
t is found that the elongated crystallographic c-axes of the films remain fully strained to the substrates for all thicknesses in both strain states. Relaxation of the a and b axes is observed for t>= 65 nm with films grown under tensile strain developing uniaxial crack arrays (running along the c axis) due to a highly anisotropic thermal expansion. For the latter films, the room-temperature in-plane electrical resistivity anisotropy, rho_b/rho_c, increases approximately exponentially with increasing film thickness to values of ~1000 in the thickest films studied. Films under tension have their Neel temperatures enhanced by ~25 K independent of thickness, consistent with an enhancement of ferromagnetic exchange along their expanded c axes.
The application of weak electric fields (<~ 100 V/cm) is found to dramatically enhance the lattice thermal conductivity of the antiferromagnetic (AF) insulator CaMnO(3) over a broad range of temperature about the Neel ordering point (125 K). The effe
ct is coincident with field-induced de-trapping of bound electrons, suggesting that phonon scattering associated with short- and long-ranged AF order is suppressed in the presence of the mobilized charge. This interplay between bound charge and spin-phonon coupling might allow for the reversible control of spin fluctuations using weak external fields.
