  The quantum kagome antiferromagnets YCu3(OH)6OxCl3-x (x=0,1/3) are produced
using a unified solid state synthesis route for polycrystalline samples. From
structural refinements based on neutron diffraction data, we clarify the
structure of the Y3Cu9(OH)18OCl8 (x=1/3) compound and provide a revised
chemical formula. We use muon spin relaxation, as a local probe of magnetism,
to investigate the exotic low temperature properties in the two compounds. In
agreement with the low temperature neutron diffraction data, we find no
evidence for long range ordering in both materials but they exhibit distinct
ground states: while disordered static magnetism develops in the x=0 compound,
we conclude on the stabilization of a quantum spin liquid in the x=1/3 one,
since the local fields remain fully dynamical. Our findings are in contrast to
previous reports based on thermodynamical measurements only. We then discuss
their origin on the basis of structural details and specific heat measurements.
In particular, the x=1/3 compound appears to realize an original spatially
anisotropic kagome model.
