By means of novel solid state electrochemical techniques the thermodynamic stability of systems comprising ternary alkali compounds can be determined without distortion of the data by electronic transference. As a particular advantage, two of the methods allow to verify in-situ the establishment and maintenance of the thermodynamic equilibria to be characterized and thus enable a sensitive differentiation between univariance and divariance of the system under consideration. (c) 2008 Elsevier B.V. All rights reserved.