By e.m.f. measurement of concentration chains concerning thallium electrode in 300–430 K temperature interval the system PbTe–TlBiTe₂ is studied. The formation of wide (to 75% TlBiTe₂) areas of solid solutions on the base of PbTe is established. From temperature dependences of e.m.f.  the partial thermodynamic functions () of thallium in alloys are calculated. On the base of solid-phase equilibriums diagram of system Tl₂Te–PbTe–Bi₂Te₃–Te the potentialformation reactions are established and standard thermodynamic functions of formation and standard entropy of solid solutions are calculated