  A quantum critical point arises at a continuous transformation between
distinct phases of matter at zero temperature. Studies in antiferromagnetic
heavy fermion materials have revealed that quantum criticality has several
classes, with an unconventional type that involves a critical destruction of
the Kondo entanglement. In order to understand such varieties, it is important
to extend the materials basis beyond the usual setting of intermetallic
compounds. Here we show that a nickel oxypnictide, CeNiAsO, displays a
heavy-fermion antiferromagnetic quantum critical point as a function of either
pressure or P/As substitution. At the quantum critical point, non-Fermi liquid
behavior appears, which is accompanied by a divergent effective carrier mass.
Across the quantum critical point, the low-temperature Hall coefficient
undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface
and a destruction of the Kondo effect. Our results imply that the enormous
materials basis for the oxypnictides, which has been so crucial to the search
for high temperature superconductivity, will also play a vital role in the
effort to establish the universality classes of quantum criticality in strongly
correlated electron systems.
