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Synthetic CaTiSiO5 and its germanium analogue (CaTiGeO5)
Mat. Res. Bull. Vol. 3, pp. 693-698, [968. in the United States.
Pergamon P r e s s , Inc.
SYNTHETIC CaTiSi05 AND ITS GERMANIUM ANALOGUE
Printed
(CaTiGe05)
C. R. Robbins National Bureau of Standards Washington, D. C., 20234
(Received June 21, 1968; Refereed)
ABSTRACT Synthetic, anhydrous CaT±S±05 (sphene) and CaTiGeO 5 are monocllnic with lattice constants a = 6.567 ± 0.005, b = 8.723 ± 0.005, ~ = 7.454 ± 0.005 8 = 119o52 ' i 2' and ~ = 6.65 ± 0.01, ~ = 8.92 ± 0.01, ~ = 7.49 ± 0.01 A, ~ = 119o45 ' ± I0' respectively. There are four formula units per cell. Cell dimensions of the silicate are close to those of natural sphene. The space group is P21/~ as compared with space group C2/! reported for natural minerals of variable composition and general formula CaTISiO 4 ( O , O H , F ) . Although x-ray intensities indicate a general structural similarity, some of the l ~ - o r d e r (h+k odd) reflections of the synthetic crystals are fairly strong, indicating appreciable shifts from the C2/! structure.
Introduct ion The crystal by Zacharlasen
structure
in 1930 (I).
composition was assumed
Crystals
sufficiently
were used in the study. monocllnlc
of the mineral
sphene
(titanlte) was determined
from Lindvikskollen,
close to the ideal formula CaT±S±05,
For this material,
unit cell with the f o l l ~ I n g
Zacharlasen
observed a
lattice constants:
a = 6.57 ± 0.01 b = 8.72 ± 0.01 ~ c = 7.45 ± 0.01 ~ = 119o43 ' .
Norway, whose
The cell volume
693
o3 (V) is 370 A •
694
SYNTHETIC CaTiS[O 5 AND CaTiGeO 5
Vol. 3, No. 8
The space group is C2/_c and the cell contains four formula units. Zachariasen concluded from examination of mineral analyses that the formula ABSiO4X(X=0,0H,F), sphene.
rather than CaTiSiO 5 could always be given for
In this formula, A and B represent cations with radius 0.67 ~ <
rA < 1.35 A and 0.57 A < rB < 0.67 A.
He observed that since most sphene
analyses showed the presence of water (presumably as OH), this might be explained by the partial replacement of oxygen in one of the three different oxygen positions, namely 01 on the dlad axes (I) o A discussion of the chemistry and a classification of sphene minerals was given by Sahama (2) who suggested that C6 (along with OH, and F) could substitute for 0 I.
He considered the following replacements to be of
importance: Calcium:
Na, Rare Earths, M_n, Sr (Ba).
Titanium: Oxygen:
A~, Fe +3, Fe +2, Mg, N-b, (Ta), V, (Cr). OH, F, (C~).
Sahama suggested CaTiSiO 4 (O,OH,F) as the ideal tltanlte formula°
He noted
that the replacement of 01 by OH,F would result in a defect structure since the amount of OH and F is independent of the replacement of Ca and Ti by other cations as shown by his analyses. The presence of fluorine in sphenes from fifteen different localities was shown by Jaffe (3). In view of the previous work on mineral samples of variable composition, it was of interest to examine single crystals of anhydrous CaTiSiO 5 obtained as part of a larger study of synthetic, sphene-like compounds. Experlmental Data I.
CaTiSiO 5 CaTiSIO 5 has been prepared in several investigations:
Fukuslma (4); Prince (5); DeVries, Roy, and Osborn (6).
Iwas~ and
It was reported to
Vol. 3, No. 8
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
695
melt congruently at 1382°C (4,6), and at 1386°C (5). Crystals were obtained for this work by slowly cooling a stolchlometric melt of high purity oxides in a platinum crucible and by growth on an iridium wire loop, both in air°
In each case, the crystals after
growth were held at 1000°C for five hours and then slowly cooled to room temperature° X-ray precession films were taken of several crystals.
Definite
reflections were observed, for example, for I01, 120, 210, 211 and many others which are forbidden in Zachariasen's space group C2/c.
No
restrictions were observed for hk~ but the following reflections were systematically absent: ho6, if h + ~ odd oko, if k odd These established the space group as P21/n as compared with C2/c for Lindvikskollen sphene. Cell dimensions and standard deviations* obtained for the synthetic sphene are: = 6.567 ± 0.005 b = 8.723 ± 0°005 c = 7.454 ± 0°005 = 119052 ' ± 2'
V = 370.3 ~3
There are four units in the cell as in Zacharlasen's structure°
Thus,
because of the difference in Bravals lattlces~ there are in synthetic sphene twice as many structural units per lattice point.
Units that are
equivalent in the mineral structure have become inequlvalent in the
* Cell parameters were refined by least squares to obtain the best agreement between observed and calculated 20 angles using the x-ray 67 system of programs developed at the University of Maryland.
~6
SYNTHETIC CaTiSiO5 AND CaTiGeO5
Vol. 3, No. 8
nthetic crystals° A differential thermal analysis of a fine powder, obtained by inding several synthetic crystals, was made at a heating rate of 10°C r minute from room temperature to the melting point°
No evidence of
lymorphlsm was observed° For comparison, x-ray precession films were taken of a mineral ecimen reported to contain one percent of H20 and of A6203 as major purities°
This crystal was found to have space group C2/_c as observed
Zachariasen.
A differential thermal analysis of the material to 1000°C
eating rate 10°C per minute) showed no indication of a phase transfortiono
However, a distinct color change from dark brown to pale yellow
ter heating was observed.
Microscopic examination showed the heated
ains were clear, transparent with optic sign unchanged (positive)°
A
alitative comparison of x-ray powder diffractometer patterns of the heated Ld unheated material gave no evidence of a structural change resulting o m this heat treatment° CaTIGeO 5 Previous synthesis of CaTiGeO 5 is unknown to the author°
Crystals
re grown on an iridium wire loop and by cooling a stoichiometric melt L a platinum crucible in air from approximately 1360°Co
As with the
licate, the crystals were held at 1000°C for five hours and then slowly ~oled to room temperature° X-ray precession films showed the same systematic absences observed ~r anhydrous, synthetic CaTiSiO 5 and, hence, the same space group (P21/~). The following cell dimensions* were observed for monoclinic CaTiGeO5:
Uncertainties given for the cell dimensions are estimates based on past experience with camera and measuring device° In the author's opinion a conservative estimate of error will be obtained if they are considered as standard deviations°
Vol. 3, No. 8
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
697
a = 6.65 ± 0.01 ~ ~ = 8.92 ± 0o01 ~ ~ = 7o49 ± 0.01 ~ o3 V = 385.7 A
= 119=45 ' ± i0'
There are four formula units per cello As may be seen by inspection, a 4°2% increase in cell volume results from the complete replacement in CaTiSiO 5 of Si IV (.42 A) by Ge IV (°53 A) to give CaTiGeO5o
The largest increase in cell dimension
is along the ~ axis (0.20 A). Discussion The data presented here suggests that the structure of anhydrous, synthetic sphene differs appreciably from that reported by Zachariasen for natural sphene minerals.
The latter should not be given the ideal
formula CaTISIO 5 because the variable OH,F or C~ content apparently plays an important role in the detailed atomic arrangement° In the author's view, pure, amhydrous CaTiSiO 5 has a distinct structure, which when fully determined, might be regarded as the parent phase.
In it there are two symmetrically inequivalent formula units
related by a [~/2 ~/2 O] translation.
If disorder amounting to a more or
less random succession of the two types of units were introduced into this structure, the resulting phase would have pseudo-sy~netry C2/~. It is quite possible that among natural sphenes of low water and halide content, one might find one with the structure of synthetic CaTiSiO 5. The author wishes to thank Eo M. Levln for the thermal analyses and H. S. Peiser for helpful discussion of the work° References I.
W. Ho Zachariasen, Z. Krist. 73, 7 (1930).
2.
Tho G. Sahama, Bullo C o n .
Geol. de Finlande, No. 138, 88 (1946).
698
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
Vol. 3, No. 8
3.
H. W. Jaffe, Amer. Min., 32, 637 (1947).
4.
K. lwas~ and M. Fukuslma, Bull. Chem. S,c. Japan, !, 91 (1932).
5.
A. T. Prince, Journ. Geol., 51, I (1943).
6.
R. C. DeVries, R. Roy, and E. F. Osborn, J. Am. Ceram. S.c., 388, 158 (1955).
Pergamon P r e s s , Inc.
SYNTHETIC CaTiSi05 AND ITS GERMANIUM ANALOGUE
Printed
(CaTiGe05)
C. R. Robbins National Bureau of Standards Washington, D. C., 20234
(Received June 21, 1968; Refereed)
ABSTRACT Synthetic, anhydrous CaT±S±05 (sphene) and CaTiGeO 5 are monocllnic with lattice constants a = 6.567 ± 0.005, b = 8.723 ± 0.005, ~ = 7.454 ± 0.005 8 = 119o52 ' i 2' and ~ = 6.65 ± 0.01, ~ = 8.92 ± 0.01, ~ = 7.49 ± 0.01 A, ~ = 119o45 ' ± I0' respectively. There are four formula units per cell. Cell dimensions of the silicate are close to those of natural sphene. The space group is P21/~ as compared with space group C2/! reported for natural minerals of variable composition and general formula CaTISiO 4 ( O , O H , F ) . Although x-ray intensities indicate a general structural similarity, some of the l ~ - o r d e r (h+k odd) reflections of the synthetic crystals are fairly strong, indicating appreciable shifts from the C2/! structure.
Introduct ion The crystal by Zacharlasen
structure
in 1930 (I).
composition was assumed
Crystals
sufficiently
were used in the study. monocllnlc
of the mineral
sphene
(titanlte) was determined
from Lindvikskollen,
close to the ideal formula CaT±S±05,
For this material,
unit cell with the f o l l ~ I n g
Zacharlasen
observed a
lattice constants:
a = 6.57 ± 0.01 b = 8.72 ± 0.01 ~ c = 7.45 ± 0.01 ~ = 119o43 ' .
Norway, whose
The cell volume
693
o3 (V) is 370 A •
694
SYNTHETIC CaTiS[O 5 AND CaTiGeO 5
Vol. 3, No. 8
The space group is C2/_c and the cell contains four formula units. Zachariasen concluded from examination of mineral analyses that the formula ABSiO4X(X=0,0H,F), sphene.
rather than CaTiSiO 5 could always be given for
In this formula, A and B represent cations with radius 0.67 ~ <
rA < 1.35 A and 0.57 A < rB < 0.67 A.
He observed that since most sphene
analyses showed the presence of water (presumably as OH), this might be explained by the partial replacement of oxygen in one of the three different oxygen positions, namely 01 on the dlad axes (I) o A discussion of the chemistry and a classification of sphene minerals was given by Sahama (2) who suggested that C6 (along with OH, and F) could substitute for 0 I.
He considered the following replacements to be of
importance: Calcium:
Na, Rare Earths, M_n, Sr (Ba).
Titanium: Oxygen:
A~, Fe +3, Fe +2, Mg, N-b, (Ta), V, (Cr). OH, F, (C~).
Sahama suggested CaTiSiO 4 (O,OH,F) as the ideal tltanlte formula°
He noted
that the replacement of 01 by OH,F would result in a defect structure since the amount of OH and F is independent of the replacement of Ca and Ti by other cations as shown by his analyses. The presence of fluorine in sphenes from fifteen different localities was shown by Jaffe (3). In view of the previous work on mineral samples of variable composition, it was of interest to examine single crystals of anhydrous CaTiSiO 5 obtained as part of a larger study of synthetic, sphene-like compounds. Experlmental Data I.
CaTiSiO 5 CaTiSIO 5 has been prepared in several investigations:
Fukuslma (4); Prince (5); DeVries, Roy, and Osborn (6).
Iwas~ and
It was reported to
Vol. 3, No. 8
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
695
melt congruently at 1382°C (4,6), and at 1386°C (5). Crystals were obtained for this work by slowly cooling a stolchlometric melt of high purity oxides in a platinum crucible and by growth on an iridium wire loop, both in air°
In each case, the crystals after
growth were held at 1000°C for five hours and then slowly cooled to room temperature° X-ray precession films were taken of several crystals.
Definite
reflections were observed, for example, for I01, 120, 210, 211 and many others which are forbidden in Zachariasen's space group C2/c.
No
restrictions were observed for hk~ but the following reflections were systematically absent: ho6, if h + ~ odd oko, if k odd These established the space group as P21/n as compared with C2/c for Lindvikskollen sphene. Cell dimensions and standard deviations* obtained for the synthetic sphene are: = 6.567 ± 0.005 b = 8.723 ± 0°005 c = 7.454 ± 0°005 = 119052 ' ± 2'
V = 370.3 ~3
There are four units in the cell as in Zacharlasen's structure°
Thus,
because of the difference in Bravals lattlces~ there are in synthetic sphene twice as many structural units per lattice point.
Units that are
equivalent in the mineral structure have become inequlvalent in the
* Cell parameters were refined by least squares to obtain the best agreement between observed and calculated 20 angles using the x-ray 67 system of programs developed at the University of Maryland.
~6
SYNTHETIC CaTiSiO5 AND CaTiGeO5
Vol. 3, No. 8
nthetic crystals° A differential thermal analysis of a fine powder, obtained by inding several synthetic crystals, was made at a heating rate of 10°C r minute from room temperature to the melting point°
No evidence of
lymorphlsm was observed° For comparison, x-ray precession films were taken of a mineral ecimen reported to contain one percent of H20 and of A6203 as major purities°
This crystal was found to have space group C2/_c as observed
Zachariasen.
A differential thermal analysis of the material to 1000°C
eating rate 10°C per minute) showed no indication of a phase transfortiono
However, a distinct color change from dark brown to pale yellow
ter heating was observed.
Microscopic examination showed the heated
ains were clear, transparent with optic sign unchanged (positive)°
A
alitative comparison of x-ray powder diffractometer patterns of the heated Ld unheated material gave no evidence of a structural change resulting o m this heat treatment° CaTIGeO 5 Previous synthesis of CaTiGeO 5 is unknown to the author°
Crystals
re grown on an iridium wire loop and by cooling a stoichiometric melt L a platinum crucible in air from approximately 1360°Co
As with the
licate, the crystals were held at 1000°C for five hours and then slowly ~oled to room temperature° X-ray precession films showed the same systematic absences observed ~r anhydrous, synthetic CaTiSiO 5 and, hence, the same space group (P21/~). The following cell dimensions* were observed for monoclinic CaTiGeO5:
Uncertainties given for the cell dimensions are estimates based on past experience with camera and measuring device° In the author's opinion a conservative estimate of error will be obtained if they are considered as standard deviations°
Vol. 3, No. 8
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
697
a = 6.65 ± 0.01 ~ ~ = 8.92 ± 0o01 ~ ~ = 7o49 ± 0.01 ~ o3 V = 385.7 A
= 119=45 ' ± i0'
There are four formula units per cello As may be seen by inspection, a 4°2% increase in cell volume results from the complete replacement in CaTiSiO 5 of Si IV (.42 A) by Ge IV (°53 A) to give CaTiGeO5o
The largest increase in cell dimension
is along the ~ axis (0.20 A). Discussion The data presented here suggests that the structure of anhydrous, synthetic sphene differs appreciably from that reported by Zachariasen for natural sphene minerals.
The latter should not be given the ideal
formula CaTISIO 5 because the variable OH,F or C~ content apparently plays an important role in the detailed atomic arrangement° In the author's view, pure, amhydrous CaTiSiO 5 has a distinct structure, which when fully determined, might be regarded as the parent phase.
In it there are two symmetrically inequivalent formula units
related by a [~/2 ~/2 O] translation.
If disorder amounting to a more or
less random succession of the two types of units were introduced into this structure, the resulting phase would have pseudo-sy~netry C2/~. It is quite possible that among natural sphenes of low water and halide content, one might find one with the structure of synthetic CaTiSiO 5. The author wishes to thank Eo M. Levln for the thermal analyses and H. S. Peiser for helpful discussion of the work° References I.
W. Ho Zachariasen, Z. Krist. 73, 7 (1930).
2.
Tho G. Sahama, Bullo C o n .
Geol. de Finlande, No. 138, 88 (1946).
698
SYNTHETIC CaTiSiO 5 AND CaTiGeO 5
Vol. 3, No. 8
3.
H. W. Jaffe, Amer. Min., 32, 637 (1947).
4.
K. lwas~ and M. Fukuslma, Bull. Chem. S,c. Japan, !, 91 (1932).
5.
A. T. Prince, Journ. Geol., 51, I (1943).
6.
R. C. DeVries, R. Roy, and E. F. Osborn, J. Am. Ceram. S.c., 388, 158 (1955).