  We investigate the mixed diamond chain composed of spins 1 and 1/2 when the
exchange interaction is alternatingly distorted. Depending on the strengths of
frustration and distortion, this system has various ground states. Each ground
state consists of an array of spin clusters separated by singlet dimers by
virtue of an infinite number of local conservation laws. We determine the
ground state phase diagram by numerically analyzing each spin cluster. In
particular for strong distortion, we find an infinite series of quantum phase
transitions by the cluster expansion method and conformal field theory. This
leads to the infinite series of steps in the behavior of the Curie constant and
residual entropy.
