Crystal structures and magnetic properties of rare-earth ultraphosphates, RP5O14 (R = La, Nd, Sm, Eu, Gd)

The single-crystal X-ray structures of lanthanum, europium, and gadolinium ultraphosphate, RP5O14 (R = rare-earth) are reported herein [monoclinic, P2 (1)/c, a = 8.8206(1), 8.7491(1), 8.7493(1) Angstrom, b = 9.1196(2), 8.9327( 1), 8.9189(1) Angstrom, c = 13.1714(2), 12.9768(2), 12.9717(1) Angstrom, be ta = 90.661(1), 90.534(1), 90.6682(3)degrees respectively; Z = 4; R1 = 0.02 50, 0.0346, 0.0270, respectively]. The structures are all type (I) compound s as classified by Bagieu-Beucher and Tranqui [Bull; Sec. Fr. Miner, Cryst. 93, 505 (1970)]. The minimum R...R separations are compared with all other structural reports of lanthanide ultraphosphates. Type (I) compounds have the lowest minimum R...R separation, which decreases with atomic number and appears not to perturb the optical properties of any rare-earth ultraphosp hate. In each case, R is surrounded exclusively by eight oxygen atoms that form a distorted square antiprism, A P-O network holds together the three-d imensional structure. The magnetic susceptibilities of neodymium, samarium, and gadolinium ultraphosphate as a function of temperature are also report ed along with corresponding magnetization measurements. All compounds exhib it a paramagnetic response, following Curie's law except in the regions whe re crystal field splittings are significant. (C) 2000 Academic Press.