July, 1933
PREPARATIOX AKD PROPERTIES OF SnFe03F
1451
PREPARATION ASD PROPERTIES OF SrzFeOJ? BY FRANCIS GALASSO AND WILDADARBY United Aircraft Corporation, Research Laboratories, East Hartford, Connecticut Received -Vovember $0,1969 Extension of the study carried out previously on KzNbQ3F has resulted in the preparation of Sr2Fe03F,mother oxvfluoride with the K2NiF4structure. Electrical measurements show that it is a p-type semiconductor which exhibits a Seebeck coefficient of 22.7 Nv./deg. A comparison of its c / a ratio and anisotropic thermal expansion with some ternary oxides having the K2NiF, structure gives some indication that the fluoride ions may be prefcrctntiall> located a t the apical positions in the anion octahedra surrounding the small cations.
Introduction Recently the preparation of K2Kb03F, an oxyfluoride with the tetragonal K2Ki17r structure, was reported b y this Lab0ratory.l Unlike ternary oxides and fluorides reported as having this structure, K&b03F exhibited a larger c / a ratio than the 3.41 value which satisfies the geometrical conditions of touching spheres. A study of the properties of this compound leads to the conclusion that the elongated “c” axis may be caused by the fluoride ions being located preferentially in the apical positions of the octahedra surrounding the small metal ions in the unit cell (Fig. 1). Continuation of this research has resulted in the preparation of another ox.yfluoride Sr2Fe03F,with the K 2 X F4 structure. The purpose of this report is to present the structural data and properties of this new oxyfluoride, in comparison with K2XF4-type strontium ternary oxides and with KZNbOBF. Experimental Investigations Preparation of Sr2FeOlF.-Powder samples of SrzFeOlF were prepared by heating mixtures of strontiuni oxide or rarbonate, strontium fluoride, and ferric oxide in a 3: 1: 1 molar ratio in a platinum crucible in air. After firing a t lOOO”, the sample was reground, pressed into a pellet, and sintered a t 1200”. The compound dissociated when heated above 1200’. Chemical Analysis .---Samples of the compound were analyzed by Ledoux and Company of Teaneck, New Jersey, for strontium, iron, and fluorine content. Anal. Calcd. for 8r2Fe03F: Sr, 58.79; Fe, 18.74; F , 6.37. Found: Sr, 57.60; Fe, 18.80; F, 6.78. X-Ray Analysis.-Powder X-ray diffraction photographs vere taken of the SrtFeOlF samples using a 114.6 mm. diameter P h i l i p powder camera with copper K a radiation. Since these X-ray patterns were similar to that of K&bOrF, one of them was indexed on the basis of th%body-centered tetragonal unit cell with a = 3.84 and c = 12.98 A. Atomic positions were adopted from space group I-4/minm (No. 139), as originally determined for K2NiFa; however, the fluoride ions were considered to be randomly distributed only in the O,O,zx, etc., positions: two iron ions a t O,O,O and 1/z,1/2,1/2; four strontium ions a t 0,O,zsr; 0,O,isr; l/p,l/2,1/2 zsr; ‘/1,1/2,1/? - Z S ? ; two fluoride and two oxygenions atO,O,zu; O,O,ix; l/A,l/%,l/~ zx; l/~,l/~,l/~ - ZX; and The relative 1/2,0,1/~. four oxygen ions at I/2,0,0; O,l/p,O; O,~/Z,~/Z; intensities of the powder diffraction lines were calculated with z g , = 0.352 and zx = 0.131, neglecting temperature and absorption effects. Table I presents calculated and observed indexing and relative intensity data. Property Measurements. Thermal Expansion.-High temperature X-ray diffractometer tracings were made between 25 and 1000’ using a Korelco diffrartometer with an attached TemPres heater. Figure 2 presents the “a” and “c” axes expansion for Sr2FeOlF and SrzTiOa. It was found that the thermal coefficient of expanqion is nearly the same in the ’‘a” and “c” directions for SrzTi01 and in the “a” direction for Sr2Fe03F, while expansion along “c” in the oxyfluoride is greater. For a0 = 1.93 X and for SrzTi04 SrzFe03Faa = 1.45 X olg = 1.46 X aC= 1.44 X Electrical Resistance.-Pellets for resistance measurements were prepared by compacting powdered SfaFeO3F in a 1.59 em.
+
--
+
(1) F. Galasdo and W. Dasby, J . Phys. Cham., 66, 1318 (1962).
die under 710 kg./cm.2 followed by sintering a t 1000”. The pellets werelsanded to flatten the surface and then plated with evaporated gold.
TABLE I POWDER X-RAYDIFFRACTION DATAFOR Sr2Fe03F sin2 6
hkl
002 101 004 103 110 112 006 105 114 200 116 107 204 008 213 206 118 220 217 208 303 310 1, 1, 10 226 314 a Diffuse.
(obsd.)
0.0141 ,0440 .OS66 .Oil9 ,0805 ,0944 ,1280 ,1372 ,1611 .2075 ,2131 ,2175 .2258 ,2333 .2885 ,3065 .32!9 ,3743 ,3863 ,3943 ,4031 .4353 ,4493 ,4589
sin’ 0 (calcd.)
0.0141 ,0438 ,0565 ,0720 ,0805 .0946 ,1271 ,1285 ,1370 1610 ,2076 ,2132 ,2175 ,2259 ,2330 .2881 ,3064 ,3220 .3742 .3869 ,3940 .4025 ,4335 ,4491 ,4590 t
I
I
(obad.)
(oalcd.)
5 5 5 100 100
