This paper focuses on the synthesis and the structure determination of two previously reported compounds of unknown structure - Ca0.96La1.56Nb1.48O7 and Ca1.16La1.26Nb1.56O7 - as well as the investigation of the center of the ternary phase diagram La2O3 – Nb2O5 – CaO. The samples are prepared by the conventional solid state ceramic route. Structure determination is performed by using microscopy electron diffraction, X-ray and neutron powder diffraction data. The formulas of the two compounds are found to be Ca2La3Nb3O14 and Ca8La8Nb14.4□1.6O56, respectively, where the symbol □ denotes cationic vacancies. Ca2La3Nb3O14 crystallizes in the rhombohedral space group R 3¯ m (No.166) (Z = 3) with the cell parameters a = 7.6525(2) (Å) and c = 18.2981(5) (Å). Ca8La8Nb14.4□1.6O56 crystallizes in the cubic space group Fd 3¯ m (No.227) (a = 10.6111(1) (Å), Z = 1). In both structures, Calcium and Lanthanum atoms are randomly distributed on the appropriate crystallographic sites. Both compounds belong to the Pyrochlore family A2B2X7. Their conduction properties are studied with complex impedance spectroscopy.The central region of the ternary diagram La2O3 – Nb2O5 – CaO, investigated using Rietveld refinements on X-ray diffraction data, is found to be composed of 8 zones which are in agreement with Gibbs rules from a thermodynamic point of view.