  The consequences of nonmagnetic-ion dilution for the pyrochlore family
Y$_{2}$($M_{1-x}N_{x}$)$_{2}$O$_{7}$ ($M$ = magnetic ion, $N$ = nonmagnetic
ion) have been investigated. As a first step, we experimentally examine the
magnetic properties of Y$_{2}$CrSbO$_{7}$ ($x$ = 0.5), in which the magnetic
sites (Cr$^{3+}$) are percolative. Although the effective Cr-Cr spin exchange
is ferromagnetic, as evidenced by a positive Curie-Weiss temperature,
$\Theta_\mathrm{{CW}}$ = 20.1(6) K, our high-resolution neutron powder
diffraction measurements detect no sign of magnetic long range order down to 2
K. In order to understand our observations, we performed numerical simulations
to study the bond-disorder introduced by the ionic size mismatch between $M$
and $N$. Based on these simulations, bond-disorder ($x_{b}$ $\simeq$ 0.23)
percolates well ahead of site-disorder ($x_{s}$ $\simeq$ 0.61). This model
successfully reproduces the critical region (0.2 < $x$ < 0.25) for the N\'eel
to spin glass phase transition in Zn(Cr$_{1-x}$Ga$_{x}$)$_{2}$O$_{4}$, where
the Cr/Ga-sublattice forms the same corner-sharing tetrahedral network as the
$M/N$-sublattice in Y$_{2}$($M_{1-x}N_{x}$)$_{2}$O$_{7}$, and the rapid drop in
magnetically ordered moment in the N\'eel phase [Lee $et$ $al$, Phys. Rev. B
77, 014405 (2008)]. Our study stresses the nonnegligible role of bond-disorder
on magnetic frustration, even in ferromagnets.
