  We present the structural, magnetic, thermal and ab-plane electronic
transport properties of single crystals of CaCu1.7As2 grown by the self-flux
technique that were investigated by powder x-ray diffraction, magnetic
susceptibility chi, isothermal magnetization M, specific heat Cp, and
electrical resistivity rho measurements as a function of temperature T and
magnetic field H. X-ray diffraction analysis of crushed crystals at room
temperature confirm the collapsed tetragonal ThCr2Si2-type structure with \sim
15% vacancies on the Cu sites as previously reported, corresponding to the
composition CaCu1.7As2. The chi(T) data are diamagnetic, anisotropic and nearly
independent of T. The chi is larger in the ab-plane than along the c-axis, as
also observed previously for SrCu2As2 and for pure and doped BaFe2As2. The
Cp(T) and rho(T) data indicate metallic sp-band character. In contrast to the
chi(T) and Cp(T) data that do not show any evidence for phase transitions below
300 K, the rho(T) data exhibit a sharp increase in slope on cooling below a
temperature Tt = 54-56 K, depending on the crystal. The \rho(T) data show no
hysteresis on warming and cooling through Tt and the transition appears to be
second order. The phase transition may arise from spatial ordering of the
vacancies on the Cu sublattice. The Tt is found to be independent of H for H
\leq 8 T. A positive magnetoresistance is observed below Tt that increases with
decreasing T and attains a value in H = 8.0 T of 8.7% at T = 1.8 K.
