Phase relations in the system SrOEu2O3-Fe2O3 and a new ternary phase Sr2EuFeO5

Phase relations in the system SrOEu2O3-Fe2O3 and a new ternary phase Sr2EuFeO5

Journal of the Less-Common Metals, 37 (1974) 281-284 ~c) Elsevier Sequoia S.A.. Lausanne - Printed in The Netherlands 281 SHORT COMMUNICATION Phase...

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Journal of the Less-Common Metals, 37 (1974) 281-284 ~c) Elsevier Sequoia S.A.. Lausanne - Printed in The Netherlands

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Phase relations in the system SrO-Eu,O,-Fe,O, M. DROFENIK,

D. KOLAR

and a new ternary phase Sr$uFeO,

and L. GOLIe

J. Stefan Institute. University of Ljubljana, 61000 Ljubljana, Jamova 39 (Jugoslavia) (Received

December

13, 1973)

The effect of various oxide additions on the magnetic and electric properties has for many years been the subject of extensive investigations. of SrFe,,O,, These oxides are either unintentionally introduced during processing or, in many instances, are deliberately added to promote densilication and to improve or modify the magnetic properties of the ceramics. Thus, an understanding of the solid-state reactions involved between magnetic phases and various oxides, and a knowledge of solid phase compatibility in these systems are of considerable importance. Previous work on the system [email protected],O, has been mainly concerned with the phase equilibria involved in the binary joins. The boundary system SrO-Fe,O, has been investigated by Batti ‘. According to him four compounds exist in the system, namely, SrFe,,O,,, Sr7Fe1,,0z2, Sr,Fe,O, and Sr,Fe,O,, of which only Sr2Fe,05 melts congruently at 1600°C. All phases except Sr,Fe,Os have compositions that are fixed or vary only within very narrow limits from their formulae. Sr,Fe,O, has a composition24 that depends on the temperature and atmosphere of the reaction. In the system Fe,O,-Eu,O, the existence of Eu,Fe,O,, and EuFeO, has been reported by several workers. Both compounds have been investigated from the magnetic and crystallographic viewpoints and are the subject of many publications on magnetic materials’. 6 The information available on the third boundary system, SrO-Eu,O,, is very limited. Blrnighousen’ reported the existence of a binary phase, SrEu,O,, having a rare-earth galeno-bismuth oxide structure. These workers have not reported on the solid solubility existing in the binary systems. Within the ternary system, the existence of two ternary phases was recently established. The compositions reported are SrEu,Fe,O,‘. lo and SrEuFeO,*. Experimental

The starting materials were reagent grade SrCO, (purity + 99.6%) Fe203 (purity 4: 99.6%) and Eu,03 (purity 99.9%). Appropriate proportions of the powdered materials were weighed, mixed, and then pressed into pellets which were pretired at 1000°C in air to decompose carbonate. The calcined pellets were crushed, mixed, re-pressed into pellets and fired in air at 1300°C for longer periods with intermittent cooling, crushing, mixing and pressing to facilitate homogeneity

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and to attain equilibrium. Temperature measurements were made with a calibrated Pt-Pt/lO% Rh thermocouple placed near the sample inside the furnace. The firing temperatures recorded were assumed to be accurate to within f 5°C. On the SrOrich side of the system samples were fired above 1400°C to increase the reactivity between the components. After firing, the pellets were cooled in air and analysed by the X-ray powder diffraction method. Equilibrium was considered to have been attained when X-ray patterns of successively fired samples showed no further change. X-ray powder photographs were obtained from a 114.6 mm diameter Debye-Scherer camera using nickel filtered CuKcc radiation. The ternary compounds, SrEu,Fe,O,, SrEuFeO, and Sr,EuFeO, were submitted to X-ray analysis with a Geiger counter diffractometer and the microstructures were analyzed to confirm that they were single phase. The melting behaviour of the compounds was investigated in a hot-stage microscope at temperatures up to 1700°C in air. Visual observation of the samples during slow heating, and the analysis of the changes in linear dimensions of the photographed samples as a function of temperature, enabled the melting temperatures of the compounds SrEu,FezO, lo , SrEuFeO, and Sr,EuFeO, to be established. The apparatus was calibrated at the melting point of a-pseudo-wollastonite (Casio,, Gel, = 1540°C) and calcium fluoride (CaF,, ce,, = 1360°C). Samples were examined thermogravimetrically up to a temperature of 1500°C to determine if there was any’non-stoichiometry due to loss of oxygen. A total number of 72 ternary compositions were fired and examined by X-ray diffraction in order to establish the sub-solidus phase relations existing in the system.

L)iscussion The published data on the binary systems were confirmed and no new phases were detected. Three ternary phases were found to exist within the system investigated. The existence of tie-lines between SrEu,Fe,O, and EuFeO,, Sr,Fe,O,, EuZ03 and a second ternary phase was established. The second ternary phase was found to have the composition SrEuFeO,, in agreement with Joubert et al.*. Further investigation established tie-lines between the SrEuFeO, and Sr,Fe,O,, EuZ03, SrEu,Fe,O,, SrEu,O, and a third, new ternary phase which was found to have the composition Sr,EuFeO,. The compound Sr,Fe,,Oz,, reported by Batti was not included in the diagram, since it decomposes ~ritectically at 1243°C’. Thermo~avimetric analysis did not indicate any loss of oxygen .from Sr,EuFeO, during heating in air at 1300°C. Analysis by Miissbauer spectroscopy indicated that only Fe3+ ions were present, thus providing further evidence that the compound is stoichiometric. All phases could be clearly resolved under the microscope. The microstructures of samples containing free SrO were difficult to prepare due to instability in air and water. Accordingly, the polishing was done in paraffin oil. Thirteen compatibility triangles were established for the system at 1300°C. It is interesting to note that all three ternary compounds lie on the EuFeO,-SrO section, as shown on Fig. 1. The melting point of SrEu,Fe,O, has previously been determined to be 159Ot_ 15°C. X-ray examination of the melted sample indicated” that the com~und

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Fig. 1. Sub-solidus equilibria compositions and tie lines.

283

in the system SrO-Eu,O,-FeaO,

showing

various

experimental

TABLE I X-RAY

POWDER

PATTERN

OF

Sr,EuFeO,

d ohm 5.632 3.661 2.940 2.912 2.813 2.408 2.361 2.150 2.012 1.834 1.810 1.746 1.709 1.642 1.628 1.546 1.521 1.508 1.461 1.412 1.393 1.343

5.632 3.660 2.940 2.914 2.8 16 2.408 2.365 2.154 2.012 1.830 1.811 1.749 1.703 1.644 1.630 1.544 1.523 1.512

1.470 1.415 1.394 1.339

002 112 121 202 004 220 123 130 132 224 215 116 400 206 042 332 240 143 422 316 334 244

10 15 50 100 30 25 70 15 10 2.5 15 10 10 30 25 15 20 20 10 10 10 10

-

dissociates on melting, since the strongest reflections of Sr,FezO, appeared together with the primary diffraction lines of the tetragonal phase, SrEuFeO, melts congruently at 1535k 15°C. The third ternary phase in this

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system, SrzEuFeOJ, melts congruently at 1540+ 15°C. The first two compounds have tetragonal structures with cell parameters a = 5.507(l), b = 19.876(2) for SrEu,FelO,10 and a= 3.87(l), b= 12.49(l) for SrEuFeO,, in agreement with published data’-lo. The crystal structure of SrEuFeO, belongs to the Z4/mmm space groups, as reported by Joubert et al. *. SrEu,Fe,O, has been determined” as belonging to the P4,Jmmm space group. The diffraction pattern of Sr,EuFeO, (Table I) was indexed on the basis of a tetragonal cell with a= 6.812 A and c= 11.265 A. With 4 formula units, the calculated X-ray density is 5.88 g/cm 3. The measured density (determined by displacement of hexane in an evacuated pycnometer) was 5.9OkO.05 g/cm3. REFERENCES P. Batti, Ann. Chim. (Rome), 52 (1962) 9-10. J. B. MacChesney, H. J. Williams, R. C. Sherwood and J. F. Potter, Mater. Res. Bull., 1 (1966) 113. P. K. Gallagher, J. B. MacChesney and D. N. E. Buchanan, J. Chem. Phys., 45 (1966) 2466. C. Brisi and P. Rolando, Ann. Chim. (Rome), 59 (1969) 5. R. S. Tebble and D. J. Craik, Magnetic Materials, Wiley, New York, 1969. M. M. Schieber, Experimental Magnetochemistry, North Holland Publ. Co., Amsterdam, 1967. H. BLrringhousen and G. Branes, Acca Cryst., 15 (1962) 1059. J. C. Joubert, A. Collomb, D. Elmaleh, G. LeFlem, A. Daoudi and G. Ollivier, J. Solid State Chem., 2 (1970) 343. 9 J. C. Joubert, D. Samaras, A. Collomb, G. LeFlem and A. Daoudi, Mater. Res. Bull., 6 (1971) 341. 10 M. Drofenik, D. Kolar and L. Gall’, J. Less-Common Metals, 30 (1973) 309. 11 M. Drofenik, D. Kolar and L. Goll’c, J. Cryst. Growth, 20 (1973) 75. 1 2 3 4 5 6 7 8