  We present a class of exact ground states of a three-dimensional periodic
Anderson model at 3/4 filling. Hopping and hybridization of d and f electrons
extend over the unit cell of a general Bravais lattice. Employing novel
composite operators combined with 55 matching conditions the Hamiltonian is
cast into positive semidefinite form. A product wave function in position space
allows one to identify stability regions of an insulating and a conducting
ground state. The metallic phase is a non-Fermi liquid with one dispersing and
one flat band.
