Partial exchange of the Li+, Na+ and K+ alkaline cations in the HNi(PO4) • H2O layered compound

The exchange of the Li+ (1), Na+ (2) and K+ (3) alkaline cations in the layered HNi(PO4) center dot H2O was carried out starting from a methanolic solution containing the Li(OH) center dot H2O hydroxide for (1) and the M(OH) (M = Na and K) hydroxides together with the (C6H13NH2)(0.75)HNiPO4 degrees H2O phases for (2) and (3). The compounds are stable until, approximately, 280 degrees C for (1) and 400 degrees C for phases (2) and (3), respectively. The I R spectra show the bands belonging to the water molecule and the (PO4)(3-) oxoanion. The diffuse reflectance spectra indicate the existence of Ni(II), d(8), cations in slightly distorted octahedral geometry. The calculated Dq and Racah (B and Q parameters have a mean value of Dq = 765, B = 905 and C = 3895 cm(-1), respectively, in accordance with the values obtained habitually for this octahedral Ni(II) cation. The study of the exchange process performed by X-ray powder diffraction indicates that the exchange of the Li+ cation in the lamellar HNi(PO4) center dot H2O phase is the minor rapid reaction, whereas the exchange of the Na+ and K+ cations needs the presence of the intermediate (C6H13NH2)(0.75)NiPO4 center dot H2O intercalate in order to obtain the required product with the sodium and potassium ions. The Scanning electronic microscopy (SEM) images show a mean size of particle of 5 mu m. The L-i+ exchanged compound exhibits small ionic conductivity (Omega cm(-1) is in the 10(-8)-10(-9) range) probably restrained by the methanol solvent. Magnetic measurements carried out from 5 K to room temperature indicate antiferromagnetic coupling as the major interaction in the three phases. Notwithstanding the Li and K phases show a weak ferromagnetism at low temperatures. (c) 2006 Elsevier Inc. All rights reserved.