  The thermodynamics of finite open antiferromagnetic XXZ chains is studied
using field theory, Bethe Ansatz and quantum Monte Carlo methods. For the
susceptibility a parameter-free result as a function of the number of sites L
and temperature T beyond the scaling limit is derived. The limiting cases T/J
>> 1/L (J being the exchange constant), where the boundary correction shows a
logarithmically suppressed Curie behaviour, and T/J << 1/L, where a crossover
to the ground state behaviour takes place, are discussed in detail. Based on
this analysis we present a simple formula for the averaged susceptibility of a
spin-1/2 chain doped with non-magnetic impurities. We show that the effective
Curie constant has a highly non-trivial temperature dependence and shows
scaling in the low-temperature limit. Finally, corrections due to intra- and
interchain couplings and implications for experiments on Sr_2 Cu_{1-x}Pd_x
O_{3+\delta} and related compounds are discussed.
