Comparative study of dissolution forms of some rare-earth iron garnet single crystal spheres

462

Jurnal of (rv~tal (iros~th 74 (1 ~66) 462464 N orth— HeMand. A iiistcrdain

LETTER TO THE EDITORS COMPARATIVE STUDY OF DISSOLUTION FORMS OF SOME RARE-EARTH IRON GARNET SINGLE CRYSTAL SPHERES F. BEREGI Research Institute for Teleconi,nunication. Gahor 4 ron-ut 65, II-102O Budapest, Hun gore

and

F. HARTMANN Research Lahoratori for (‘restal Phisic. Hungarian Academy of ,S’ciencev, Budadrsi ía 45. 11-1112 Budape,. Hungary Received 7 October 1965

Single crystal spheres of rare-earth iron garnets (R Fe

5~

where R

dependence of the dissolution forms on the chemical composition

=

Yb. Fr. Ho, Y. Gd. Sm) have been dissolved in acids. The

i~ discussed.

It was shown by Bennema et al.. in their paper on the topological or applied graph theoretical analysis of garnet [1]. that the relative morphological importance of the dominant forms of garnet crystals depends on the chemical composition. This paper presents an experimental investigation of the dependence of the dissolution forms of rare-earth iron garnet crystals on the chemical composition. Our dissolution experiments were carried out on R 5Fe5O~~ (RIG) single crystals, where R = Yb. Er. Ho, Y. Gd. Sm. The crystals were grown from PhO--PbF~---B2O5 melt flux in the temperature range 1200—1000°C with a cooling rate of 0.5—1°C/h. The as-grown crystals were hounded by {211} and { 110) faces. The inclusion-free single crystals chemically analysed, theirpowder lattice constantswere were determined by theand X-ray

The dissolution loriiis were investigated h’5 a .JEOL JSM-35 scanning detector electron microscope. An optical goniometer was used for mdcxing the crystal faces. After a few hours’ dissolution in I-I P04 at 150°C’{111 } ~. octahedron faces and {100} i) cube faces appeared on the single crystal spheres of YhIG and ErIG (fig. Ia). Under similar conditions, the single crystal spheres of HoIG. YIG, GdIG and SmIG. however, were hounded h~’ { hkO} i) tetrakishexahedron faces besides the { 111)1) octahedron faces. Final dissolution forms with {100) ~ faces were obtained in the cases of YhIG and ErlG crystals. while the final dissolution forms of HolG, YIG, GdIG and SmIG crystals were bounded by the faces of tetrakishexa310}i) and hedra indices {720}~). {3lO}i)with (figs. lb and{SlO}i). ic). It can he seen{ from table

method. From these crystals, spheres with a diameter of 0.8 mm were prepared, which were dis-

I that there is a connection among the lattice constants (a 0 ). the radii of the rare-earth ions (r~ ) and the final dissolution fornis of the investigated garnet crystals. The increase of the radii of the rare-earth ions and the increase of the lattice constants imply a change in the Miller indices of the final dissolution forms, namely a monotonous decrease of the h/k ratio for the final dissolution forms.

solved either in concentrated H5P04 at 150°C’ or in azeotropic HBr at 126°C’. The preparation of the spheres and the dissolution technique were the same as in ref. [2]. Dissolution experiments on crystal plates with hollow semispheres were also carried out using the same solvents,

0022-0248/86/$03.50 Elsevier Science Publishers By. (North-Holland Physics Publishing Division)

E. Beregi, 12. Hartrnann

/

I), mo/ulion form

f RI(; mingle rital yhi’res

463

•

~

Fig. I Dissolution forms of rare-earth iron garnem spheres in

HP0 4 at 150°C:(a) {I00} I) and (111 } ~ faces on Yh5Fe5O12: (b) (5I0}~faces on Ho5Fe5O12 (c) {310}~)on Gd5Fe5O12. Markers represent 0.1 mm.

On the dissolution of a hollow semisphere on a YbIG single crystal plate in H1P04, only (211) faces were observed, in while the of dissolution of hollow semispheres, the on cases GdIG and YIG, single crystal plates beside the (211) faces (100) faces appeared too. These facts are in good agreement with the theory of Lacmann et al. [3].

According to their theory, if the equilibrium form consists of only (211) faces,fIlO}i) on theand dissolution 100}t)’ (111) i) form may appear { faces, and the final dissolution form is a cube with (100) faces at the condition that h(V~ 1) < I. The { hk0} D faces may only appear, however, if the equilibrium form consists of two or more types of faces. —

464

L Bereg,, L llartoiann

Iii

i/un

mi

6 pin

1 RI (, ‘in gii /

iii

p/i

m

Table I Final dissolution forms of rare-earth iron garnets in H

5P04 at

150°C Composition

r~5[4] (nm)

a0 (nm)

Final dissolution form

Ratio h/k

Yh5Fe~O1~ Fr5Fe~O1~ Ho Y 5Fe5O~~ 5Fe5O~2 2 (jd5Fe~O1 Sm 5Fe5O1~

0.1125 0.1144 0.1155 0.1159 01193 0.1219

1.23023 1.23474 123751 123765 124712 1.25293

{iOO}i) 100)p)

~ 5.0

{510}i)

________

{

{72O}~ 1I0}i) { {310} I)

3.5 10 3.0

~ ~

I ig. ~. Pati ‘I .i liolloss ‘~eini~phcrc on Gd I e ( )~ .r~~i,il pl.iie dis’,ol’.ed in IIBr it 121 ( \laiker repre~enKii I nun

do not seem to depend on the chemical composition. There was no significant difference on the dissolution of hollow semispheres in HBr either. Usually (110) faces were formed with rough sections. which obviously do not correspond to equilibrium faces (fig. 3). Thanks are due to J. Làbâr for SEM investigai’ I )i’.’oluiuon hi in at Sin .1 ~ )~ ~in~le ~rs~ial~plicre Ii Br at I 21 ( M,irker reple~cnt~ Ill mm

tions and to F. Tanos for taking part in the experimental work.

On the dissolution of rare-earth iron garnet spheres in HBr. both (100) i) and { ~ } m~ were formed. The (100) i) faces were rather significant in every case (fig. 2). The surfaces of the crystals

References

were rough with a lot of terraces, in contrast to the surfaces of crystals dissolved in HmPO4. The Ill) ~ face on fig. 2 is built up from terraces of (110) faces. We could not obtain the final dissolution form with one kind of face for either of the rare-earth iron garnets hut YIG [2]. The dissolution forms of the crystal spheres dissolved in HBr

[1]P. Bennema. E.A. Giess and J.E. Weidenhorner. I Crystal

21 13]

Growth 62(1983)41. F, Beregi. F. Hartniann, I L~uhàr.F Sterk and I Tanos. I Crystal Growth 65 (1983) 562 RLacmann, W Franke and R Heimann. J. Crystal Grosmih 26 (1974) 107

4j BK

Vainshtein, VM

Fridkin and VL Indenhoni. Mod-

em Crystallography II: Struciure of (‘rvsials (Springer. Berlin, 1982) pp. 78-81.