Vol. 8, No. 9, September 1969
OXIDESHAVING THE CORUNDUM STRUCTURE 1985
the cubane-type structure alkoxide oxygens are above the faces of the copper(I1) tetrahedron and in the p4-oxo structure there is an oxygen a t the center of the tetrahedron and a chloride above each edge; the close relationship between the bonding in these two types of structures has been discussed.12
Acknowledgments.-This work was supported by N S F Grant GP-7406. The help of the Rich Electronic Computer Center of Georgia Institute of Technology with computations is gratefully acknowledged. (12) S. F. A. Kettle, Theorel. Chim. Acta, 4, 150 (1966).
1315 FROM THE CENTRAL RESEARCH DEPARTMENT, EXPERIMENTAL STATION, E. I. DU PONT DE XEMOURS AND COMPANY, WILMINGTON, DELAWARE19898
CONTRIBUTION NO.
The C Rare Earth Oxide-Corundum Transition and Crystal Chemistry of Oxides Having the Corundum Structure BY C. T. P R E W I T T , R. D. SHAXNON, D. B. ROGERS,
AND
A. W. SLEIGHT
Received December 2, 1968 Syntheses of new corundum-type phases a t a pressure of 65 kbars show t h a t complete solid solubility exists 111 the systems In203-T1zOa, In203-Fee03, and Fe203-Ga203. Sc203 is soluble in In203 up to a ratio of about 1:1. A structure refinement of In203 I1 resulted in average interatomic distances essentially the same as those found for In203 I. Attempts to refine the structure of T1203 I1 were not successful. Consideration of t h e structural relationships among corundum, B rare earth oxides, and C rare earth oxides and comparison of electronegativity differences between 111203 and t h e rare earth oxides suggests why In208 and T I 2 0 3 transform to the corundum structure whereas Sc~03,Y203, Lu203, and TmpO3 transform to the B rare earth oxide structure a t high pressure. Plots of effective cationic volume vs. unit cell volume, normalized c / a ratios vs. d-electron configuration, and metal-metal distances v s . effective ionic radii for gll corundum-type phases provide a better understanding of the crystal chemistry of corundum-type oxides. Int'eratomic distances and c / a ratios are shown to be consistent with the Goodenough model which correlates electrical properties with metal-metal interactions. In addition, these correlations have been used to predict individual interatomic distances in the Rhz03 structure.
Introduction Several simple oxides are known to occur with the corundum (a-A1203)structure, including A1203,TizO3, vzo3, Cr203, Fe203, Ga203, and Rh203.' Recently, high-pressure transformations of In203and which normally have a C rare earth oxide structure, to a modification with the corundum structure2 have been reported. 3 , 4 The corundum modification a t high pressure was unexpected in that the usual high-pressure transformation observed for compositions with the C rare earth oxide structure is to the B rare earth oxide form. Hoekstra5 found that even a t intermediate pressures corundum structures are not formed for any of the rare earth oxides. Since density increases in the order C -+ corundum + B, i t was not clear why the rare earth oxides are never found in a corundum modification, while In203 apparently never adopts the B form.6 In order to attempt resolution of this problem, we have investigated the effects of pressure on the (1) R. W. G. Wyckoff, Crystal Sluuct., 2 , 8 (1964). (2) Throughout this paper, "corundum structure" will refer t o any phase considered t o be isotypic with a-AliOa. T h e low-pressure forms (C rare earth or bixhyite structure) of Inz08 and T I 2 0 8 will be referred to as In208 I and Tho8 I. T h e high-pressure phases with the corundum structure will be referred t o as InzOa I1 and T I 2 0 8 11. (3) R. D. Shannon, Solid State Commun.,4 , 629 (1966). (4) A. N. Christensen, N. C. Broch, 0. V. Heidenstam, and A. Nilsson, Acta Chem. Scand., 21, 1064 (1967). ( 5 ) H. R. Hoekstra, Inorg. Chem., 5 , 754 (1966). (6) InzOa, recently subjected t o 120 kbars and 900", still retains the corundum structure: A. F. Reid and A. E. Kingwood, J . Geophys. Res., 7 4 , 3238 (1969).
simple oxides Sc203, Y z 0 3 , Lu203, Tm203,and Mn203 and on the ternary systems In203-T1203,Fe203-Ga2O3, InzO3-Fe2O3,and In203-Sc203. We have also refined the structure of In2O311. Consideration of the results of this work in relation to the structures of the three available modifications provides a reasonable explanation for the high-pressure stabilization of the particular oxide phases in question. Least-squares refinements of the structures of the following oxides have been reported : A 1 ~ 0 3 Ti203,798 ,~ V203,7Cr203,7Fe203,789 GazQ3,'O and 1 1 1 2 0 3 . ~ The availability of new crystallographic data for In203I1 and T120311, whose existence considerably broadens the stability field of known corundum phases, now provides a basis for considering the general crystal chemistry of corundum-type oxides. Such a consideration is also facilitated by the recent derivation of a set of ionic radii," which appear to permit more reliable generalization. Accordingly, we present in the discussion of our work a n attempt to correlate systematically the relations between observed structural parameters, chemistry of the various cations, ionic radii, and physical properties for the oxides that are known to have the corundum structure. Finally, the correlation of struc(7) R. E. Newnham and Y.M. de Haan, Z. Krist., 117, 235 (1962). (8) S. C. Ahrahams, P h y s . Rev., 180, 2230 (1963). (9) R. L. Blake, R. E. Hessevick, T. Zoltai, and L. W. Finger, A ~ J S . Mineralogist, 51, 123 (1966). (10) M. Marezio and J. P. Remeika, J. Chem. P h y s . , 46, 1862 (1967). (11) R. D. Shannon and C. T. Prewitt, A d a Cryst., B25, 925 (1969).
TABLE I CRYSTAL DATAFOR OXIDESHAVING THE CORUXDUM STRUCTURE
Effective ionic radius I,
A
Y3,
La
0 53 0 615
0.149 0.233
0 6%
0.238
0 64
0,202
0 645
0,268
0 665 0 67
0.294 0 , 801
--
Cell dimensions,
& A
a
C
cia
759 i 1 961 f 1 954 9825 5 9791 6 9793 4 952 i 1
12.991 i 5 5 13.599 13.584 13.433 1 13.437 i 4 13,429 14.002 =t5
2.73 2.74 2.74
5.0345 5 0351 f 3 5 108 5 149 z 1 5 1572 j ,2
13 13 13 13 13
4 4 4 4 4 4
+ +
*
+
i49 750 =k 1 81 642 f 8 600 f 1
2.70 2.83
2 73 2 70
o3
Unit cell vol, A3
Electron confign
Electrical properties
254.80 289 85 288.72 288.80 288.49 288 34 297.36
2pG 3d3
Insulator, E
3dX0
Insulator, E
301 301 312 313 313
3@
80 88 05 23
> 8 eVJ
Ref
a a C
=
-1- 8 e\')
b
e c
3dL
idb
Semiconducting, metallic transition a t ~ 1 5 0 " KpK'r , % ohm crn" Insulator, piyr E 10J3 ohm cm"
a
a e d
Semiconducting, a,i metallic transition e at 200°, PRT 2 10-1 ohm cmo 14 510 + 1 2 64 378 33 4d'O 0,193 5,4870 i 3 Semiconductor,h e 0 7Y E = 3 8 e\14 851 =t1 2.58 424.77 5dX0 e Metallic?, pic'r = lOF 0.681 5.7168 3 0 88 oh1r1 CIllB 'LR . E. Neivnham and Y , M. d e Haan, 2.K h t . , 117, 235 (1962). * M . Marezio and J. P.Remeika, J . Chew. Phys., 46, 1862 (1967). I. H. E. Swanson, N. T. Gilfrich, and G . M . Ugrinic, "Standard X-Ray Diffraction Patterns," Sational Bureau of Standards Circular 539, U. S.Government Printing Office, Washington, D. C . d A. Wold, R . J. Arnott, and W. J. Croft, Inorg. Chenz., 2, 972 (1963). D a t a obtained in this work. T i 2 0 3crystals were kindly supplied by P.Raccah and T. Reed, Lincoln Laboratories, M.I.T.,Lexington, Mass. f H. H. Tippins, Phys. Rev., 140A, 316 (1965). Q F. J . Morin, Pizys. Rea. Letters, 3, 34 (1959); F.J. Morin, Bell Sysfein Tech. . 130, 2230 (1963). J . , 37, 1047 (1958). h R . L. Weiher and R . P. Ley, J . A p p l . Phys., 37, 299 (1966). * S.C. Xbrahams, P h ~ s Rev., 3di
26
+
t u r d parameters with effective ionic radii is used to predict interatomic distances in the unrefined RhzO3 structure.
carried o u t on crystals of InsO;i I1 and is reported below. Resistivity data were obtained by the four-probe method on single crystals of In203 I1 and InScOa I1 and on polycrystalline samples of T120311, T11n08 11, and IiiI'e03.
Experimental Section
Synthesis and Properties of High-pressure Corundum Phases Table I1 lists some of the new corundum-phase products and their properties. Table 111 lists calculated and observed d values and observed intensities for In20a11 and T120311. In203.-Hoekstra5 found that In203a t pressures up to 60 kbars and temperatures of 550, 1000, and 1430" retained the C structure. Since the smaller rare earth (RE) oxides showed transitions to the R structure a t high pressures, Hoekstra prediced a similar transition for In203. Early experiments a t 63 kbars and 1000° with mixtures of 1nzO3and Co metal resulted in transparent brown crystals 0.05mm in diameter. X-Ray powder patterns indicated the corundum structure (Inz03 11). Later experiments with pure I n 2 0 3resulted in formation of I1 a t temperatures as low as 800" if the sample had first been preheated to 1250". If no preheating had occurred, formation of I1 took place only above 1000". The presence of 2% EuaOa completely inhibited the transformation a t 1200". Crystals of In203 I1 grown a t temperatures from 800 to 1300" were transparent and colorless. Crystals grown above 14Wo developed a deep blue color, \rhich could be bleached by heating iI1 air a t 500' for several minutes;. Presuniably the blue color is caused by oxygen deficiency. Crystals of Inz03I1 approximately 0.3 mm in diam-
Starting materials were oxides obtained froin Spex Inc. and purity except for T1203 and Sc?03which were , respectively. Ternary oxide mixtures were prepared by blending the oxides in alcohol, drying, and remixing dry. T h e process' was repeated several times before pelleting the samples at 20,000 psi. These pellets were placed in cylindrical P t holders, encased with a BiV sleeve and covers, and placed inside a graphite sleeve, which served as a heater. This assembly was then placed in a pyrophyllite tetrahedron. The reactions were carried out in a tetrahedral anvil press whose operation and ~ all cases the samcalibration were described b y Bither, et ~ 1 . ' In ples were pressurized to either 65 or 89 kbars, heated t o the reaction temperature, and allowed t o react for 1hr. The samples were quenched to room temperature in less than 60 sec by turning off t h e pow-er. T h e pressure was then released slowly (3-4 min). T h e samples recovered from these runs were frequently composed of hexagonal prismatic crystals whose dimensions were approximately 0.2 X 0.5 mm. X-Ray powder patterns mere obtained a t 25' on a de WolffGuinier camera; d values were calculated using X(Cu K a i ) 1.54051 b with a KC1 internal standard (a = 6.2931 A). Table I lists cell dimensions obtained from a least-squares refinement of these data. Cell dimensions of GaaOJ, Pen03, and TLOs were obtaiiied in order to verify previously obtained literature values. T h e samples of Ga%03 and Fe203 were prepared in highly crystalline form by heating at 65 kbars and 1100O for 1 hr. T h e sample of Ti203 was prepared by Reed, et al.13 Chemical analysis of this sample indicated a stoichiometry of TiOl,50r. Cell dimensions of other samples of TiO, where x > 1.503 show considerable variation from the values reported here. A structure refinement was (12) T, A. Bither, J. L. Gillson, and H. S. Y o u n g , I i r o i g . C h e ~ i i . 5, , 1550 (1966). (13) T. B. Reed, I
