The structure of the glass phase in Rb1-x(NH4)xH2PO4

X-ray measurements on the glass state of Rb 1-x (NH 4 ) x H 2 PO 4 have been made for x=0.78, 0.75, 0.72, 0.68 and 0.49. The results show short-range antiferroelectric ordering for x>0.70 which disappears on warming above 60K. There is also evidence for a tendency to order with a wave-vector, q=( zeta , 0, 0), with zeta approximately 0.35a*. The tendency increases with decreasing x and largely disappears on warming above 160K.