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)·H2O was carried out starting from a methanolic solution containing the Li(OH)·H2O hydroxide for (1) and the M(OH) (M=Na and K) hydroxides together with the (C6H13NH2)0.75HNiPO4·H2O phases for (2) and (3). The compounds are stable until, approximately, 280 °C for (1) and 400 °C for phases (2) and (3), respectively. The IR spectra show the bands belonging to the water molecule and the (PO4)3− oxoanion. The diffuse reflectance spectra indicate the existence of Ni(II), d8, cations in slightly distorted octahedral geometry. The calculated Dq and Racah (B and C) parameters have a mean value of image, image and image, 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)·H2O phase is the minor rapid reaction, whereas the exchange of the Na+ and K+ cations needs the presence of the intermediate (C6H13NH2)0.75HNiPO4·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 μm. The Li+ exchanged compound exhibits small ionic conductivity (Ω 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.