Single crystals of the double phosphate Na2PbP2O7 have been prepared by melting using phosphate flux. Na2PbP2O7 is of triclinic symmetry with the space group P (1) over bar (Z = 2), the unit cell parameters are a = 5.533(4) Angstrom, b = 6.942(4) Angstrom, c = 9.440(4) Angstrom, alpha = 105.58(2)degrees, beta = 97.03(4)degrees, gamma = 108.32(4)degrees, d(cal) = 4.386 g cm(-3). The lattice of Na2PbP2O7 consists of corner-shared structural units [Pb2P4O14](4-) which form ribbons parallel to the [010] direction. The [Pb2P4O14](4-) units result from the association of corner-shared PbO5 polyedra and P2O7 pyrophosphate groups. The Na+ ions are located between ribbons. Glasses with the same composition as the crystalline phase have been also isolated. A study of transport properties of Na2PbP2O7 in the crystalline and glassy forms is reported. (C) 2000 Elsevier Science BN. All rights reserved.