William Joseph James

Dielectric Properties of Solid Solutions of BiFeO3 with Pb(Ti, Zr)O3 at High Temperature and High Frequency

Solid solutions of BiFeO3 with PbTiO3, PbTi0.5Zr0.5O3, and PbZrO3 were prepared. The crystallographic data on these solutions, which are basically perovskitic, are given. The dielectric constants of the materials were determined at a frequency of 0.53 GHz and at temperatures up to 800°C. Dielectric Curie points were found in solutions containing up to 90 mole % BiFeO3. These results leave little doubt that BiFeO3 is ferroelectric or antiferroelectric. The extrapolated Curie point for BiFeO3 is above 850°C. BiFeO3 appears more likely to be ferroelectric than antiferroelectric, but the distinction between the two classifications may not be sharp.

Magnetic behavior of rare-earth iron-rich intermetallic compounds

The thermal variation of lattice parameters of rare earth-transition metal intermetallic compounds rich in Fe, Co or Ni in the temperature range of 25-900°K is studied. For the Fe compounds, negative thermal expansion is observed below their magnetic ordering temperatures regardless of the nature of substitutional ordering. For Co and Ni compounds, the thermal expansion behavior is normal. It is then concluded that for the Fe compounds, the magnetic properties are mainly determined by the Fe-Fe interatomic distances and the number of Fe nearest neighbors, whereas for Co and Ni compounds the magnetic properties are determined by the conduction electron transfer from the rare earth to the 3d band of Co or Ni, The anomalous thermal expansion of Fe compounds and the metamagnetic transition of the Lu compound is explained in terms of the distance dependence of the interaction energy as proposed by Neel.

Magnetic interactions in R/sub 6/Mn/sub 23/ rare earth intermetallics

Polarized neutron experiments on a single crystal of Y6Mn23 give evidence for a ferrimagnetic arrangement of Mn atoms. The value of the Mn moment depends on the crystallographic site. Magnetization measurements at low temperature suggest non‐collinear magnetic structures for single crystals of Gd6Mn23, Dy6Mn23, and Er6Mn23. The non‐collinearity results from the effects of negative R‐R interactions and the crystal field.

Magnetic and crystallographic properties of SmMn/sub 6-x/Fe/sub x/Ge/sub 6/ intermetallics

The magnetic and crystallographic properties of induction-melted SmMn/sub 6-x/Fe/sub x/Ge/sub 6/ compounds, where x is 0, 0.5, 1.0, and 1.5, have been studied using X-ray diffraction and bulk magnetic measurements between 30 and 490 K. All of the samples crystallized in the YCo/sub 6/Ge/sub 6/-type structure with the space group P6/mmm. A small amount, less than 9 mol%, of Sm(MnFe)/sub 2/Ge/sub 2/ was present as an impurity in all samples. The unit cell volume decreases with increasing iron content at an average rate of 2.4% per substituted atom at room temperature. The a and c lattice parameters decrease at an average rate of 1.1 and 0.1% per substituted atom at room temperature, respectively. The magnetic properties deteriorate rapidly as the iron concentration increases beyond x=0.5. Magnetic behavior of SmMn/sub 5/Fe/sub 1/Ge/sub 6/ and SmMn/sub 4.5/Fe/sub 1.5/Ge/sub 6/ is indicative of antiferromagnetic or ferrimagnetic coupling. According to X-ray diffraction patterns of magnetically aligned powders, the easy direction of magnetization at room temperature for all of the samples lies close to the basal plane of the unit cell.

Ferroelectric Properties of PbZrO3–BiFeO3 Solid Solutions

Solid solutions of BiFeO3 and PbZrO3 were investigated for crystallographic and dielectric properties. A new pseudocubic perovskite phase was found, which has been tentatively indexed as orthorhombic with the same unit cell as PbZrO3 but with dielectric properties characteristic of a ferroelectric substance. The Curie point in this series of solid solutions has a minimum of about 155°C at a composition of about (PbZrO3)0.80 (BiFeO3)0.20, which at room temperature lies on the boundary between the orthorhombic antiferroelectric and the pseudocubic ferroelectric phases. This composition has a relative dielectric constant of 800 at room temperature and shows appreciable dielectric nonlinearity. The Curie point rises to about 400°C for (PbZrO3)0.50 (BiFeO3)0.50 and is extrapolated to about 900°C for pure BiFeO3, in agreement with previous data from similar solid solutions. It is felt that this is additional evidence that the distortion from cubic symmetry in BiFeO3 may be of ferroelectric origin.

Voltammetric Evaluation of Zinc Electrowinning Solution Containing Nickel

The effect of nickel impurity in zinc sulfate electrowinning solutions was studied using voltammetry techniques. The reactions occurring at various points on the polarization curve are proposed and comparisons made for both pure electrolyte and those containing nickel. A nickel‐activated hydrogen evolution peak was found to occur at low current densities during the anodic sweep portion of the curve, the height of which was found to be proportional to the nickel concentration in solution. The influence of certain operating parameters such as zinc ion concentration, potential scan limit, and scan rate on the nickel activated peak was also determined.

Magnetic properties of substituted R 2 (Fe, Al, Co) 14 B compounds

The effects of the substitution of Fe by Al in R 2 (Fe 1-x Al x ) 14 B compounds (R = Y, rare earths) on their magnetic properties have been investigated. The compounds crystallize in the tetragonal structure, P4 2 / mnm, provided x 1 , and the anisotropy field, H A , exhibit a maximum at x = 0.06. The substitution of Fe with Al atoms is also effective in enhancing the coercivity of magnets based on the Nd-Fe-B compounds. As the Y atom carries no magnetic moment, the increased anisotropy field must result from preferential ordering of the non-magnetic Al atoms among the six non-equivalent crystallographic sites of the iron sublattice. Earlier work has shown that the replacement of Fe by Co results in increasing the Curie temperature and decreasing the coercive field. The present data show that the Nd-(Fe, Al,Co)-B magnets have both high Curie temperatures and high coercive forces. Accordingly, it appears that it is possible to improve the thermal properties and reduce the total losses of Nd-Fe-B magnets by appropriate substitution of Fe with Al and Co atoms.

Structural and magnetic properties of intermediate oxygen stoichiometry PrBa2Cu2Ox

Abstract The compound PrBa 2 Cu 3 O x ( χ ∼ 7) is non superconducting and exhibits antiferromagnetic ordering of the Pr moments at a relatively high temperature of about 17 K. We have investigated the structural and magnetic behavior of PrBa 2 Cu 3 O x for two different oxygen contents ( x = 6.9 and 6.4). Magnetic susceptibility measurements show that both these compounds are ordered antiferromagnetically with Neel temperatures of 15.7 and 12.5 K and effective paramagnetic moments of 2.85 μ B and 2.94 μ B for x = 6.9 and x = 6.4 samples, respectively. The susceptibility (χ) of the x = 6.4 sample shows a pronounced peak typical of antiferromagnetic systems unlike the x = 6.9 sample where χ shows only a slight break and continues to rise even below T N .

Perfection of the Lattice of Dislocation‐Free Silicon, Studied by the Lattice‐Constant and Density Method

The lattice‐constant and density method revealed that a high‐purity silicon crystal free of dislocations has a perfect lattice without an excess of vacant sites or interstitials (n′=8.00004) within the limits of error, in agreement with the results obtained with the decoration method. The lattice constant of vacuum heated silicon powder of semiconductor purity was 5.43070±0.00004 A; that of the nonheat‐treated powder was 5.43081 A at 25°C. The constants determined from crystal chips by the rotating crystal method were lower: between 5.43028–5.43048 A at 25°C. As the constants of each series of measurements could be reproduced very well (s=±0.00004 A), the lower values suggested the presence of some unknown systematic errors, the magnitude of which is outside the scope of errors due to absorption. The thermal expansion coefficients of all samples between 10°–60°C were (2.6±0.4)×10−6/°C. The average density of etched crystal chips was 2.3289±0.0001 g/cm3. The lower density of the nonetched chips indicated t...

Neutron diffraction and magnetic studies of Nd/sub 2/Fe/sub 17-x/T/sub x/ (T=Si, Mn) alloys

We have carried out neutron and magnetic studies on Nd/sub 2/Fe/sub 17-x/T/sub x/ (T=Si, Mn) alloys. The unit cell of the compounds contracts with both Si and Mn substitution. Si atoms avoid the 6c site, prefer the 18h site strongly, fill the 9d site steadily and fill the 18f site only at relatively high Si concentration. Mn atoms avoid the 9d sites but prefer the 6c site strongly, while the 18f site and 18h site fill slowly. The Si site occupancies appear to be dominated by the crystal environment while the Mn site occupancies are dominated by steric considerations. The Curie temperature of the compound Nd/sub 2/Fe/sub 17/ increases significantly with Si substitution but is only affected slightly by the Mn substitution. Although the unit cell contracts with increasing Si concentration, the average length of bonds to the Fe(6c) and the Fe(18f) sites increase slightly at x<4.