  We report on the synthesis and the physical properties of Ba1-xRbxTi2Sb2O (x
< 0.4) by x-ray diffraction, SQUID magnetometery, resistivity and specific heat
measurements. Upon hole doping by substituting Ba with Rb, we find
superconductivity with a maximum Tc = 5.4 K. Simultaneously, the
charge-density-wave (CDW) transition temperature is strongly reduced from T_CDW
55 K in the parent compound BaTi2Sb2O and seems to be suppressed for x > 0.2.
The bulk character of the superconducting state for the optimally doped sample
(x = 0.2) is confirmed by the occurrence of a well developed discontinuity in
the specific heat at Tc, with \DeltaC/Tc = 22 mJ/mol K2, as well as a large
Meissner-shielding fraction of approximately 40 %. The lower and the upper
critical fields of the optimally doped sample (x = 0.2) are estimated to
\mu0Hc1(0) = 3.8 mT and \mu0Hc2(0) = 2.3 T, respectively, indicating that these
compounds are strongly type-II superconductors.
