The crystal habit of uranium dioxide

JOTJRNAL

OF KilTCLEAR

5, No. 2 (1962) 262- 263, KORTH-HOLLAND

MATERIALS

PUBLISHING

CO..

AMSTERDAM

THE CRYSTAL HABIT OF URANIUM DIOXIDE R. UKAEA

G. ROBINS

t, R.

S. WILKS

Research Croup, Metallurgy Division, Atomic Energy Research Establishment, Harwell, Didcot, Berka, UK

Received

1.

28 Sept.

Introduction

The close relationship between morphology and the detailed symmetry of atomic arrangement has been demonstrated by observations of the crystal habit of uranium dioxide. Single crystals of the oxide, prepared by several available production routes, were used for these investigations. 2.

and B. T. BRADBURY

1961

(111) (100) (3311, and (111) (100) (113) (See figs. 2 and 3). Electron microscopy of fractured surfaces of polycrystalline uranium oxide, sintered to den-

Experimental Observations

The crystal habit of uranium dioxide single crystals was found to differ slightly, depending upon the method of preparation. Vapour deposited crystals had a (Ill} (100) habit 1) (fig. 1). Electrolytically deposited crystals had a habit which was dependent on the concentration and composition of the electrolyte 23s). The three observed habits were {Ill) {loo},

Fig.

1.

V&pour deposited

the predominant t

{ill}

Present address:

crystals

habit.

of UOa showing

2. (111)

Fig. 3. {ill)

(Crystal size 0.1 mm).

University

Fig.

College, Wollongong, 262

N.S.W.,

Electrodeposited (100)

(331)

habit.

Electrodeposited {IOO) (113) Australia.

habit.

crystal

of

UOa

showing

(Crystal size 3 mm).

crystal

of

UOz

showing

(Crystal size 1 mm).

THE

sities of

94 O/Otheoretical,

CRYSTAL

HABIT

revealed

spherical

pores in grain interiors, some of which exhibited well developed planes on their surface 4+ Some of these grain interior pores or “negative often exhibited very pronounced crystals” growth markings, which were indexed as (111) {loo}

(110)

Fig. 4.

837) (see

“Negative

fig.

crystal”

4).

in sintered UO2 showing

{ 11 l} { 100) { 1 IO} habit of growth markings. Electron micrograph.

OF

of

URANIUM

smallest

3.

Remarks

The Donnay-Harker Principle 9) which is a modification of the Bravais Law, states that the crystal-forms which tend to form most frequently are those with faces parallel to planes

area,

taking

into

con-

planes in the various space groups. Consideration of these two principles results in the same deduction, when those space groups containing no screw axes or glide planes are present, as is the case with uranium dioxide, (space group Fm3m). The forms in order of decreasing importance for space group Fm3m are: (1 ll} (100) (110) (311) (331). Various combinations of all these forms have been observed in uranium oxide (section 2). Thus, the observations reported here for uranium dioxide, provide evidence that the habit of a crystal species is determined by both the particular space group pattern on which the structure is built, and the external environment during crystalhsation.

References 1)

x 30 000.

uranite crystals are or (100) (110) orien-

reticular

sideration the presence of screw axes and glide

J. T. Waber,

J. A.

J. Electrochem. 2) R.

Naturally occurring usually of (110) (111) tation 8).

263

DIOXIDE

a) 4)

G. Robins,

R. 8. Wilks,

UKAEA

(1961)

T.

Padden,

R.

96

3 (1961)

(Harwell)

294

Report,

Westinghouse

A. Portnoff-Porneuf,

6)

B. T. Bradbury,

7)

S. Takahashi,

(USA)

AEREReport,

J. Nut.

Mat.

2 (1960)

181

to be published

et al., J. Atomic.

Energy Sot. Japan

73

*)

C. Frondel,

9)

J. D. H. Donnay 22 (1937)

Mat.

586 (1959)

5)

2 (1960)

and R. Kleinberg,

106 (1959)

J. Nut.

R 3833 WAPD-T

O’Rouke

Sot.

Geological 73

Survey

Bull.

and D. Harker,

1064 (1958)

Amer. Mineral.