Ternary Eu pnictides EuTX (T = Ni, Pd, Pt; X = P, As) are mixed valent
and undergo one or two first-order phase transitions in dependence of
temperature. At the phase transitions the Eu valence changes by about
1/6. The phase transitions are connected with an unusual behaviour of
the lattice constants. The observations are explained within a model
of electrostatically charged layers.