An investigation of structural, magnetic and dielectric properties of R2NiMnO6 (R = rare earth, Y)

We have investigated the structure, magnetic and dielectric properties of the double perovskite oxides, R2NiMnO6 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Y). We could refine powder X-ray diffraction patterns of all the phases on the basis of monoclinic (P2(1)/n) double perovskite structure where Ni and Mn atoms are ordered at 2c and 2d sites, respectively. All the phases are ferromagnetic insulators exhibiting relatively low dielectric loss and dielectric constants in the range 15-25. The ferromagnetic ordering temperature of the R2NiMnO6 series seems to correlate better with the radius of R3+ atoms than with the average Ni-O-Mn angle (phi) in the double perovskite structure. These results are consistent with all samples having Mn4+ and Ni2+ With minimal antisite disorder.

Ammonium ions prevent methylation of uridine to ribothymidine in Azotobacter vinelandii tRNA

It was shown that tRNA from Azotobacter vinelandii grown in the presence of ammonium chloride lacks ribothymidine while that grown in the absence of the ammonium salt contains this modified nucleoside. [32P]-Labelled tRNA from this organism grown in a medium containing the ammonium salt was digested with RNase T1 and the pseudouridinecontaining tetranucleotide, common to all tRNAs was isolated and analysed for the nucleoside replacing the ribothymidine. It was found to be uridine. Cells previously labelled with [32P]- phosphate in the ammonium salt medium were washed and incubated in the ammonium saltfree medium to test whether ribothymidine would be formed upon removal of the ammoniumions. Methylation of the uridine did not take place.

Satellites in the X-ray photoelectron spectra of transition-metal and rare-earth compounds

An attempt has been made at synthesis and in resolving some of the uncertainties related to the assignments of charge-transfer satellites in the X-ray photoelectron spectra of transition-metal and rare-earth compounds. New satellites are reported in the ligand core-hole spectra as well as in the metal core-level spectra of oxides of second- and third-row transition metals including rare earths. Satellites in the ligand levels and the metal levels tend to be mutually exclusive, a behaviour that can be understood on the basis of metal-ligand overlap. Systematics in the intensities and energy separations of satellites in the first-row transition-metal compounds have been examined in order to gain an insight into the nature of these satellites. A simple model involving the sudden approximation has been employed to explain the observed systematics in intensities of satellites appearing next to metal and ligand core levels on the basis of metal-ligand overlap.

A Magnetic Susceptibility Study of Spin-state Transitions in Rare-earth TrioxocobaItates( III)

Rare-earth trioxocobaltates(lll), Ln[CoO,], with Ln = Pr, Nd, Tb, Dy. and Yb exhibit low-spin to high-spin transitions of cobalt characterised by a maximum in the Ax-l against temperature plots where Ax is the cobalt contribution to the magnetic susceptibility. The susceptibility behaviour is distinct from that of La[CoO,] which shows a plateau in the x-I-T curve accompanied by a structural transition. The temperature at which the AX- I-T curve shows a maximum increases with the decrease in the size of the rare-earth ion. The susceptibility behavior of solid solutions of La,,Nd,CoO, has been investigated to see how the behaviour characteristic of Nd[CoO,] changes to that of La[CoO,].

Facile conversion of electron rich benzylic hydrocarbons to carbonyl compounds by peroxydisulphate and copper ions

A convenient method for the conversion of electron rich benzylic hydrocarbons to carbonyl compounds is reported.

X-ray crystal and molecular structure of a hydrated lithium picrate complex of benzo-15-crown-5; An example of non-chelation of the crown

Complexation of alkali and alkaline earth metal ions with crown ethers is well known (1) and chemical and crystallographic studies have been carried out for number of complexes (2,3). The interaction of the metal with the crown ether depends on the nature of the cation and particularly on the basicity of the anion (4) , In this paper we report the crystal and molecular structure of a lithium picrate complex of benzo-15-crown-5, the first x-ray crystallographic study of a lithlum-crown system.

Gibbs energies of formation of rare earth oxysulfides

The standard Gibbs energy change accompanying the conversion of rare earth oxides to oxysulfides by reaction of rare earth oxides with diatomic sulfur gas has been measured in the temperature range 870 to 1300 K using the solid state cell: Pt/Cu+Cu2S/R2O2S+R2O3‖(CaO)ZrO2‖Ni+NiO, Pt where R=La, Nd, Sm, Gd, Tb, and Dy. The partial pressure of diatomic sulfur over a mixture of rare earth oxide (R2O3) and oxysulfide (R2O2S) is fixed by the dissociation of Cu2S to Cu in a closed system. The buffer mixture of Cu+Cu2S is physically separated from the rare earth oxide and oxysulfide to avoid complications arising from interaction between them. The corresponding equilibrium oxygen partial pressure is measured with an oxide solid electrolyte cell. Gibbs energy change for the conversion of oxide to the corresponding oxysulfide increases monotonically with atomic number of the rare earth element. Second law enthalpy of formation also shows a similar trend. Based on this empirical trend Gibbs energies of formation of oxysulfides of Pr, Eu, Ho, and Er are estimated as a function of temperature.

Factors affecting localized abundance and distribution of lesser mealworm in earth-floor broiler houses in subtropical Australia.

Factors that influence the localized abundance and distribution of lesser mealworm, Alphitobius diaperinus (Panzer), in litter of two compacted earth-floor broiler houses in subtropical Australia were studied using various experimental manipulations. Numbers of lesser mealworms substantially increased inside caged areas and under uncaged empty feed pans placed in open areas of the houses. These populations were found to be localized and independent of chicken-feed, manure, and high beetle populations that normally occur under existing feed pans. Substantial horizontal movement of larvae to under feed pans was recorded. Placing metal barriers around these pans significantly restricted this movement. In almost all treatments, lesser mealworms typically peaked in numbers during the middle of the flock time. This temporal pattern of abundance also was observed under pans within barriers, where relatively low insect numbers occurred, but it was not observed in uncaged open areas (where chickens had complete access). It is likely that larvae do not establish in open areas, but fluctuate in numbers as they either move to refuges away from chickens or suffer high rates of mortality. In these refuges, larvae peak in numbers and then leave the litter environment to pupate in the earth floor before the end of the flock time. This behavior might be exploited for management of lesser mealworm by targeting applications of control agents.

Earth song as storywork: Reclaiming Indigenous knowledges

Is it possible for Indigenous ways of knowing, which draw on earth song and storywork, to find a place within the academy? Indigenous peoples recognise that the earth has a song, which we can listen to as story. In return, we can sing our story to the world and of the world. In this paper, the authors explore their own stories and songs. They explain the ways that listening to the earth’s song and working with stories can inform their work in the academy – as teachers who support younglings to hear their voices and develop their own songs, and as the writers and tellers of curriculum. The authors ask whether it is possible for Indigenous academics to combine their academic work with Indigenous ways of knowing. They argue that, not only is the combination possible, it can be used to create a harmonious voice that will help them to reclaim their power as Indigenous academic women.

High temperature stability of oxysulfides containing Ce3+ and Y3+ ions

Standard Gibbs energies of formation of oxysulfides of cerium and yttrium from their respective oxedes were determined using solid oxide galvanic cells incorporating calcia-stabilized zirconia as the electrolyte in the temperature range 870–1120 K. The sulfur potential over the electrode containing the oxide and oxysulfide was fixed by a buffer mixture of Ag + Ag2S. A small amount of CaH2 was added to the buffer to generate an equilibrium ratio of H2S and H2 species in a closed system containing the buffer and the electrode. The sulfur potential is transmitted to the electrode via the gas phase. The results can be summarized by the equations 2left angle bracketCeO2right-pointing angle bracket+1/2(S2)→left angle bracketCe2O2Sright-pointing angle bracket+(O2) ΔG°=430600−109·7T(±400)J mol−1 left angle bracketY2O3right-pointing angle bracket+1/2(S2)→left angle bracketY2O2Sright-pointing angle bracket+1/2(O2) ΔG°=114780−1·45T(±200)J mol−1 The values are compared with data reported in the literature. The stability field diagram for the Ce---O---S system has been developed using the results of this study for Ce2O2S and data for other phases from the literature.

ESR and optical studies of Mo5+ and W5+ ions in phosphomolybdate and phosphotungstate glasses

ESR and optical studies of phosphomolybdate and phosphotungstate glasses are discussed. Both the ESR and optical results indicate that molybdenum or tungsten ions are present in distorted octahedral environments in these glasses. In addition, ESR spectra of Mo5+ and W5+ ions show that the d electrons are localized on molybdenum and tungsten sites respectively. The variation of gperpendicular and gshort parallel values has been examined using appropriate structural models of these glasses.

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems. In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given. In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.

Estimation Of Properties Of Rare-Gas Solids From Compression Characteristics Of Closed-Shell Ions

We present a unified approach to repulsion in ionic and van der Waals solids based on a compressible-ion/atom model. Earlier studies have shown that repulsion in ionic crystals can be viewed as arising from the compression energy of ions, described by two parameters per ion. Here we obtain the compression parameters of the rare-gas atoms Ne. Ar. Kr and Xe by interpolation using the known parameters of related equi-electronic ions (e.g. Ar from S2-. Cl-, K- and Ca2-). These parameters fit the experimental zero-temperature interatomic distances and compressibilities of the rare-gas crystals satisfactorily. A hightemperature equation of state based on an Einstein model of thermal motions is used to calculate the thermal expansivities, compressibilities and their temperature derivatives for Ar. Kr and Xe. It is argued that an instability at higher temperatures represents the limit to which the solid can be superheated. beyond which sublimation must occur.

Complexes of Rare-Earth Metals with Meconic Acid

Two series of complexes of meconic acid (H3 Mec) with rare-earths have been prepared by varying the preparative procedure. The compounds have the general formulae, [Ln(Mec) (H2O)2]·3 H2O (whereLn=La, Ce, Pr, Nd, Sm, Ho and Y) and [Ln(HMec) (H2 Mec) (H2O)2]·4 H2O (whereLn=La, Pr, Nd and Sm). The infrared spectral data indicate that the carboxylate groups are bound to the rare-earth metal in a bidentate fashion. Thermal studies indicate that two water molecules are coordinated in each case. The complexes are probably polymeric.

Oxidation of alkaline earth sulfides to sulfates: Thermodynamic aspects

The emf of the galvanic cell, Pt, Ni + NiO/(CaO) ZrO2/MS + MSO4, Ir, Pt, where M is calcium, strontium, or barium, has been measured in the temperature range 850 to 1100 K. From these measurements the Gibbs’ energy changes for the oxidation of sulfides of alkaline earth metals to their respective sulfates have been calculated. The results are compared with available thermodynamic data in the literature. The agreement varies from ±2 kJ for the strontium system to ±20 kJ in the case of barium. Trends in the stabilities of alkaline earth sulfates are discussed in relation to the properties of the cationic species involved.