Neutron diffraction investigation of U3O8

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Submitted on 1 Jan 1964

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Neutron diffraction investigation of U3O8

B.O. Loopstra

To cite this version:

B.O. Loopstra. Neutron diffraction investigation of U3O8. Journal de Physique, 1964, 25 (5), pp.429-

430. �10.1051/jphys:01964002505042900�. �jpa-00205798�

429.

NEUTRON DIFFRACTION INVESTIGATION OF U3O8 By ^{B. O. LOOPSTRA} (1),

Reactor Centrum Nederland, Petten, ^the Netherlands.

Résumé. 2014 Un échantillon polycristallin d’U3O8 orthorhombique ^{a été} étudié par diffraction

neutronique ^afin d’essayer d’expliquer certaines différences apparues lors de deux études précé- dentes faites l’une sur un monocristal aux rayons X et l’autre par diffraction neutronique. Le groupe

d’espace est Amm2 - (C142v). Les atomes d’uranium sont entourés par six oxygènes ^{en contact}

situés à des distances comprises ^entre 2,07 ^et 2,23 Å ; les atomes d’uranium ont un septième

voisin oxygène ^{situé à} 2,44 Å pour U1 ^et 2,71 Å pour U2.

Abstract.

A polycrystalline sample ^of orthorhombic U3O8 ^{has been} investigated by ^neutron

diffraction in order to resolve discrepancies ^between previous single crystal X-ray ^and powder

neutron investigations. The spacegroup is found to be Amm2 - (C142v). The uranium atoms

are surrounded by ^six oxygens in close contact at distances between 2.07 and 2.23 Å, ^{with a}

seventh oxygen ^{at 2.44} Å for the U1 and ^{at 2.71 Å for the} U2 ^atoms.

LE JOURNAL DE PHYSIQUE ^10ME 25, ^MAI 1964,

A polycrystalline sample of orthorhombic U308

has been investigated by ^neutron diffraction in order to resolve discrepancies ^{between a} previous single crystal X-ray investigation (Chodura ^and

FIG. 1.

(1) ^Work sponsored jointly by Reactor Centrum Neder-

land, ^The Netherlands, and Institutt for Atomenergi, Noway.

Mal~) ^{and a} powder ^neutron diffraction inves-

tigation (Andresen), ^the difference with the pre- vious investigation being ^{a much} higher resolution.

In the present investigation the unit cell axes were found to be a

4.148 ~., ^b

11.966 ^A

and c

6.717 us. Here, ^{the axes are chosen in}

accordance with the usual space group designation.

The cell dimensions _agree with Andresen’s data,

but Chodura and Maly ^{find an a-axis ot double} length. ^{No trace is found in the neutron} diagram

of this nor of the monoclinic splitting ^{of the reflec-} tions, also noticed by Chodura and Mal~. ^In

agreement ^{with both} previous investigations, ^the

cell is centered in the (100) ^{face. This leaves as} possible space groups A222(D2), A2mm(Cg§), Amm2(C2") ^and Ammm(D"). ^{A fourier} projec-

tion along ^the a-axis, ^{made with the Okl neutron}

intensities _up to (015) ^as observed values and with Andresen’s parameters ^{to obtain the calculated} signs, ^shows clearly ^{that the correct} space group is Amm2. From this point ^on the structure was

refined by ^{trial and error} methods down to

TABLE

PARAMETERS U30, (Amm2)

In the final structure (see figure ^and table) ^each uranium atom is surrounded by ^six oxygens ^at

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01964002505042900

430

distances between 2.07 and 2.23 A. One out of the three uranium atoms of U308 ^{has a seventh}

oxygen ^at 2.44 A, ^{the other two have a seventh}

oxygen ^at 2.71 A. This would seem in agreement with the composition ^{U6+ U2+ O8 .}

The full paper will appear ^{in Acta} Crystallo- graphica.

°

Discussion

Dr IBERS.

Pouvez-vous expliquer ^le blocage apparent ^{d’un atome} par ^une anisotropie ^{de vibra-}

tion ? Comment traitez-vous 1’agitation ^ther- mique ?

Dr LOOPSTRA. - Les facteurs de temperature isotropes ^sont appliqu6s ^{a U} (2But = 0,46 ui2) ^et

0 (2Bo = 1,38 ~.2). L’anisotropie de vibration

devrait être très grande pour l’oxyg6ne ^en (0, 1/2)

dans la projection ^de Fourier, et, cependant ^n’ex- pliquerait pas pourquoi ^le pic (U + 0) ^en (0, 0)

serait si peu élevé.

Dr BERTAUT. - Dr Ibers pense ^{a un} modele d’oscillateur anharmonique. ^On pourrait ^v6rifier

par ^une simple experience. Avez-vous fait un dia- gramme ^{a très} basse temperature ?

Dr LOOPSTRA.

Non.

Dr. HOLTZBERG. - Avez-vous fait des mesures

de densité ? Elles sont excellentes pour verifier la

stoechiométrie.

Dr LOOPSTRA.

Non.

~

’

REFERENCES ANDRESEN (A. F.), ^Acta Cryst., 1958, 11, ^612.

CHODURA (B.) ^{and MALY} (J.), Second United Nations

International Conference Peaceful Uses of Atomic

Energy, 1958, ^vol. 23, ^223.