Stig Rundqvist

Determination of the homogeneity range and refinement of the crystal structure of Fe2P

Abstract The homogeneity range of Fe2P has been determined using the annealing and quenching technique in combination with X-ray powder diffraction methods. The iron-rich limit is invariant at Fe2.00P for temperatures up to 1150°C. The phosphorus-rich limit varies from Fe2.00P at low temperatures to Fe1.94P at 1100°C. The crystal structure of Fe2.00P has been refined from X-ray diffraction data obtained by single-crystal diffractometry. The thermal vibrations differ appreciably in magnitude for the two non-equivalent types of iron atom.

First order magnetic transition, magnetic structure, and vacancy distribution in Fe2P

Abstract The para- to ferromagnetic transition in Fe 2 P has been studied using Mossbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μ B and 1.78 μ B for Fe(1) and Fe(2), respectively. An assignment of the components in the Mossbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra. The ordering of metal vacancies has been investigated by a Mossbauer study of a nonstoichiometric Fe 2 P sample and by an X-ray diffraction study of a nonstoichiometric Mn 2 P crystal.

Mössbauer study of phosphides containing iron

Abstract A series of binary and ternary transition metal phosphides containing iron has been investigated by Mossbauer spectroscopy. Most of the compounds studied show complex magnetic behaviour, and interpretations are proposed for some cases. The crystallographic ordering mechanism in Me 2 P-type phosphides is discussed, and it is shown that great care must be taken in assigning the observed components of the Mossbauer spectra to the various crystallographic positions of the iron atoms.

First Order Magnetic Phase Transition in Fe2P

The magnetic properties of stoichiometric Fe2P and non-stoichiometric Fe2-xP (0 < × ≤ 0.06) have been studied by means of magnetic susceptibility. Measurements on pure stoichiometric Fe2P samples show that there is a first order magnetic phase transition from a ferro- to a paramagnetic state at 216 ± 1 K. The transition is accompanied by a discontinuous change in the dimensions of the hexagonal unit cell with a decrease in the a-axis of 0.06% and an increase in the c-axis of 0.08% for increasing temperature. The transition is interpreted to be of magnetoelastic origin with an exchange energy critically sensitive to the interatomic spacing. Measurements on single crystals show that the spins are directed along the hexagonal c-axis with an exceedingly high axial anisotropy. The saturation moment is 1.46 μB/iron atom and the anisotropy energy as estimated from low field data is ~ 2.5 × 106 J m-3 (2.5 × 107 erg cm-3). The transition behaviour is very sensitive to the magnitude of the external field as well as to the presence of impurities and deviations from the ideal stoichiometry in the samples.

Hydrogen and deuterium in transition metal-p element compounds: Crystal chemical aspects of interstitial solid solubility and hydride phase formation☆

Abstract Compounds of transition metals with p elements of groups IIIb–VIIb which have been reported to exhibit hydrogen-absorbing properties are surveyed. Hydrogen is taken up only by those materials that have metallic properties or contain metal clusters with delocalized bonding. Almost all p elements can be constituents of these materials, and at least one transition metal component which is itself capable of dissolving hydrogen or forming hydride phases must be present. The crystallography of the hydride phases is presented and discussed with particular emphasis on results obtained by neutron diffraction methods. The hydrogen atoms are accommodated either in interstitial solid solutions with only minor changes in the host lattices or in new phases formed by major rearrangements of both transition metal and p element atoms. The distribution of the hydrogen atoms on the interstitial sites in the structures appears to be governed by two empirical rules: the hydrogen atoms are always more than 2 A apart and they preferentially occupy those sites that are most distant from the p element atoms.

A Mossbauer study of the (Fe1-xMnx)2P system

Structural and magnetic changes with composition in the (Fe1-xMnx)2P system with 0.01 0.70 and with the orthorhombic Co2P-type structure for 0.26<x<0.68. Manganese substitutes preferentially for iron at the Fe(2) position in both the Fe2P and Co2P structures. Magnetic hyperfine fields, centroid shifts and quadrupole splittings are reported, as well as the results of magnetisation measurements for (Fe0.97Mn0.03)2P at 4.2K in fields up to 12 T.

A Mössbauer and X-ray study of Fe2P1−xBx compounds (x < 0.15)

Abstract Boron/phosphorus substitution in Fe2P has been studied by 57Fe Mossbauer spectroscopy. The magnetic ordering temperature increases rapidly with increasing boron content. Replacement of a phosphorus atom by boron in the immediate environment of an iron atom results in a substantial increase of the magnetic hyperfine field, while the centroid shift and the quadrupole splitting are almost unchanged. The hyperfine parameters for iron atoms at larger distances from the boron atom remain unaffected. Boron substitutes preferentially for phosphorus at the singlefold P(2) position in the Fe2P structure.

Coordination and bonding in representatives of the Fe3P-, Ti3P-, α-V3S- and β-V3S-type structures

Abstract A survey of the atomic coordination in the compounds concerned is presented in the form of histograms showing the number and distribution of interatomic distances. This survey reveals certain systematic coordination trends. These are found to correspond to trends in the cohesive strength of the elemental transition metals. On this basis an empirical rule for phosphide representatives can be formulated as follows: the greater the cohesive strength of the parent metal, the smaller is the phosphorus coordination number in the corresponding phosphide. An attempt is made to rationalize this rule in terms of current theories for the chemical bonding in compounds between transition metals and nonmetals with unfilled p levels.

Specific heat and magnetic susceptibility of single phase YBa2Cu3O7

Abstract The specific heat of a single phase sample of the high T c superconductor YBa 2 Cu 3 O 7 has been measured. The specific heat jump at T c (91.6 K) is found to be ΔC e / T c =59 mJ / mol K 2 , which is considerably larger than previously reported values. From low field magnetization measurements the width of the transition of our sample is found to be 0.4 K.

A neutron diffraction investigation of deuterated Pd3P0.80

The crystal structures of pure and deuterated Pd 3 P 0.80 have been analyzed by Rietveld-type profile refinements of neutron powder diffraction intensity data. Pd 3 P 0.80 crystallizes with the cementite (Fe 3 C)-type structure, space group Pnma (No. 62), Z =4, with random vacancies at the phosphorus positions. In Pd 3 P 0.80 D 0.15 (equilibrium composition at 296 K and 500 kPa D 2 pressure), the deuterium atoms occupy sites near the vacant phosphorus positions. The deuterium atoms have five palladium neighbors (average D-Pd distance 2.14 ) in a distorted square pyramidal coordination.