  The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore
lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation.
We show here that the solid solutions LiGa1-xInxCr4O8 between these two
'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and
structural transitions upon doping the end members, (ii) spin-glass-like
freezing above 2 K in the range 0.1 $\lesssim$ x $\lesssim$ 0.6, and (iii)
apparent spin-gap behavior for x $\gtrsim$ 0.7. Furthermore, no transitions are
observed above 2 K at x ~ 0.9, where magnetic susceptibility remains finite at
2 K and magnetic heat capacity shows a quadratic temperature dependence at 1-5
K. Our work shows that breathing pyrochlore compounds provide a unique
opportunity for studying both geometrical frustration and bond alternation.
