Sonication accelerated formation of Mg-Al-phosphate layered double hydroxide via sol-gel prepared mixed metal oxides

Single-phase magnesium-aluminium layered double hydroxide (LDH) intercalated with dihydrogen phosphate was successfully produced by hydration of nanopowder of the respective mixed metal oxide (MMO) obtained using sol-gel based method followed by a two-step anion exchange hydroxide-to-chloride and chloride-to-phosphate. The MMO with the metal cation ratio of Mg/Al = 2:1 was prepared using the aqueous sol-gel method. Processes of the parent Mg2Al-OH LDH formation and the successive anion-exchanges, ОН- → Cl- and Cl- → H2PO4-, were considerably accelerated via the application of high-power (1.5 kW) ultrasound. The crystalline phases formed at all stages of the Mg2Al-H2PO4 LDH production were characterized using X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Based on the data of chemical analysis and the XRD data, the type of the intercalated phosphate anion was determined and the arrangement of this anion in the interlayer was modelled.publishe

High-power ultrasonic synthesis and magnetic-field-assisted arrangement of nanosized crystallites of cobalt-containing layered double hydroxideu

High-quality stoichiometric Co2Al–NO3 and Co2Al–CO3 layered double hydroxides (LDHs) have been obtained by precipitation followed by anion exchange, both high-power sonication assisted. Application of high-power ultrasound has been demonstrated to result in a considerable acceleration of the crystallization process and the anion-exchange reaction. Two independent approaches were used to form bulk and 2-D samples of Co2Al–NO3 with the oriented crystallites, namely uniaxial pressing of deposits from sonicated LDH slurries and magnetic field assisted arrangement of LDH crystallites precipitating on glass substrates. A convenient way of preparation of semi-transparent compacts with relatively big blocks of oriented crystallites have been demonstrated. Thin dense transparent films of highly-ordered crystallites of Co2Al–NO3 LDH have been produced and characterized.publishe

Magnetic anisotropy in the CoII-AlIII-nitrate layered double hydroxides with the Co/Al ratios 2, 3, and 4

It is shown that the difference in the CoII and the AlIII ionic radii and a random distribution of the Co ions in the metal hydroxide layers of layered double hydroxides (LDHs) result in a series of highly distorted Co(OH)6 octahedral complexes. The distortions have been modelled by accounting for the Shannon ionic radii of metals and ligands. The energy of the four low lying Kramers doublets and its g-factors were calculated for all the Co-complexes. The statistical distribution of the distorted octahedra types has been shown to vary with cations content. It was found that the g-factors of the lowest Kramers doublets are highly anisotropic with different orientations of their main axes. The calculated broad range of the g-factor distribution is illustrated by the observed anomalies of the low temperature electron paramagnetic resonance response. The impact of the relative cations content n = (1-x)/x = CoII/AlIII on the nanoparticles aspect ratio of the [CoII1-xAlIIIx(OH)2]x+(NO3)- x·zH2O LDHs has been considered.publishe

High-temperature electrical conductivity of the xNBT–(1-x)LMT ceramics: verification of Meyer-Neldel rule

Electrical conductivity behaviour of x(Na0.5Bi0.5)TiO3-(1-x)La(Mg0.5Ti0.5)O3 ceramics with x ranging from 0.95 to 0.8 was analysed in the temperature range from 300 K to 800 K at microwaves (1MHz – 1GHz frequency region). Analysis of calculated DC conductivity parameters has shown that the activation energy changes at about 690 K which could be associated with the phase change in these materials. The logarithm of preexponential factor of DC conductivity changes linearly according to the activation energy, i.e. it follows Meyer-Neldel rule both below and above the phase transition point.publishe