This note is dedicated to Professor D.A. Tayurskii on the occasion of his 60th birthday
Double perovskite Sr 2CoNbO 6-δ was obtained using a novel pyrolysis method involving nitrate-organic mixtures of the corresponding components and studied by means of XRF, magnetization-based, and EPR methods. The oxygen content equal to 5.4 was obtained from X-ray fluorescence analysis and magnetization data. The effective magnetic moment is 4.05μB per cell, that corresponds to the theoretical values. The phase transition to an ordered state in the temperature range of 5÷300 K was not detected. The antiferromagnetic nature of exchange interactions between the spins of cobalt ions is confirmed by the negative sign of the Curie-Weiss temperature Θ=-50 K obtained via fitting the inverse magnetic susceptibility. An exchange-narrowed line from cobalt ions is observed in the EPR spectrum in the temperature range of 5÷80 K. A sharp increase in the linewidth at 80 K is associated with the dynamic Jan-Teller effect
Coordination biopolymers, namely, nickel complexes of sodium pectate, have been actively studied in recent years as promising representatives of non-platinum catalysts for proton exchange membrane fuel cells. The structure of coordination polymers consisting of natural precursors is complex and not entirely regular. It presents significant difficulties in determining the internal structure of coordination polymers. Identifiable electron paramagnetic resonance (EPR) signals of various Mn2+ units in sodium pectate manganese complexes have provided important structural information in systems similar in composition to nickel coordination biopolymers. In addition, the manganese complexes with the natural pectin polymers themselves are of interest as non-platinum PEMFC catalysts
Hydroxyapatite (HAp)-based materials doped with rare earth elements (REE) have shown applications as biomaterials, lighting emitting materials, scintillating materials, in vivo imaging probes, and thermoluminescent dosimeters. Gadolinium-containing calcium phosphates are promising contrast agents for various bioimaging modalities. In this work, hydroxyapatite materials with gadolinium ion impurities with a 0.44 mol.% concentration were obtained by wet chemical precipitation. Samples after chemical synthesis (as-dried) and heat treatment were studied using electron paramagnetic resonance (EPR) spectroscopy in continuous wave and pulsed modes. Analysis of the EPR spectra made it possible to establish the incorporation of Gd 3+ ions in the structure of HAp in two calcium positions with different parameters of the spin Hamiltonian. Heat treatment of samples at a T = 1300°C leads to a significant change in the EPR spectra of Gd 3+ ions with a decrease of the uncontrolled nitrate anion centers (synthesis by-product) concentration
