  Two kinds of electroconvection (EC) patterns in an ether-bridged bent-core
nematic liquid crystal material (BCN), which appear in different frequency
ranges, are examined and compared in this paper. One is a longitudinal pattern
with the stripes parallel to the orientation of the BCN and with a periodicity
of approximately the cell thickness, occurring in the high frequency range of
several hundreds Hz; the other one is oblique stripes, which results in a
zig-zag pattern, and appears in the low frequency range of several tens Hz. In
addition, within an intermediate frequency range, transformations from oblique
to longitudinal and then to normal stripes occur at increased ac voltages. In
particular, we investigated the temperature behavior of longitudinal and
oblique stripes: when the temperature T increases and approaches the clearing
temperature Tc, the contrast of the domains is enhanced and the frequency range
of existence becomes wider, while the onset voltages increase only moderately
instead of diverging, thus suggesting an isotropic mechanism of pattern
formation.
