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Crystal stoichiometry of Czochralski grown rare-earth gallium garnets
Journal of Crystal Growth 26(1974)169 170
C
North-Holland Publishing Co.
CRYSTAL STOICHIOMETRY OF CZOCHRALSKI GROWN RARE-EARTH GALLIUM GARNETS C. D. BRAN DLE* and R. L. BARNS Bell Laboratories, Murray Hill, New Jersey 07974, U.S.A. Received 18 July 1974; revised manuscript received 19 August 1974 The observed lattice parameters of Czochralski grown rare-earth gallium garnets are reported and were found to be larger than those of stoichiometric ceramic samples. The difference is attributed to some of the rare-earth ions occupying the octahedral site which results from a shift ofthe congruent melting composition toward the rare-earth rich region of the phase diagram. The degree of octahedral rare-earth substitution was found to be a function ofthe ionic radius and ranges from x 0.01 for Nd 3Ga5O12 to x 0.09 for Y3Ga,O12 in (RE3 lRE~Ga2 0]Ga30i2).
In this letter we report on the observed difference between the lattice parameters of pulled rare-earth gallium garnets and those of ceramic samples reported in the literature. We attributed this difference in lattice parameter to the rare-earth ion partially occupying the octahedral site in4)theand garnet structure’ Schneider et 3), al.5) have Carruthersnon-stoichiometric et al. examined ceramic samples of Gd 3Ga5Oi 2 and Y3Ga5O~2 respectively and concluded that there exists a solid solution range of the rare6)earth has in the garnet structure. Gellersample measured the density of aFurthermore, non-stoichiometric of Y 3 [Y0 69Ga1 3flGa3O1 23and concluded is + for Ga3 + inthat the there garnet a direct substitution of Y structure as opposed to an oxygen gallium Vacancy. All crystals were grown from stoichiometric melts, i.e., a 3:5 using mole ratio of the rare earth oxidemelts to containing gallium oxide, the growth furnace, sample pretreatment and conditions reported earlier for gadolinium gallium garnet7’8). Lattice parameters were measured at 25.0 °Cby the HPM method9) on
are used in the garnet structure, the departure of the single crystal lattice parameter from the observed powder data becomes more pronounced. Using the data in table 1 along with the literature data from ceramic samples, one can calculate the 2 ~
250
-
~ ~
2.40 230
--
~
220
2 IC
~ SINGLE CRYSTAL DATA
0
~ ‘t
0.96
1b 0.98
I
~m
.00
Y
1°
i~b I
.02
I 04
~
I
06
IONIC RADIUS
1.08
110
I
~jd
F~r
112
114
(A)
6) versus rare-earth Fig. 1. Lattice parameters of single crystals grown from stoidodecahedral ionic radius. chiometric melts and literature powder data TABLE I
Composition of garnets RE 3[RE~,Ga2 stoichiometric melts~]Ga3O12grown from
etched samples taken from the top of each of the crystals. The uncertainty (3 a) in the lattice parameter is about 0.0002 A. The results of these measurements are given in table 1 and shown graphically in fig. 1. In addition, fig. 1 shows a linear least squares fit of both the 6). single As crystal data and previous ceramic literature data can be seen from the figure, as smaller rare earth ions Present address: Union Carbide Corporation, San Diego, California 92123, U.S.A. *
169
Rare earth Nd Sm Eu Gd Tb” Dy Ho Y
r
10)
0.995 0.964 0.950 0.938 0.923 0.908 0.894 0.892
a0~(crystal)
Aa0
x
12.5090 12.4384 12.4084 12.3831 12.3486 12.3196 12.2957 12.2945
0.003 0.005 0.006 0.007
0.0l~ 0.018 0.022 0.027
0.013 0.0I4~’) 0.020
0.056 0.063 0.091
Ceramic data not available. ~ A(CuKo 1) 1.540562 A. *
170
C. D. BRANDLE AND R. L. BARNS
the crystal from stoichiometry increases. These results suggest that the solubility of the rare-earth ion in the
01 o I-
resulting in a shift ofthe congruent melting composition
08
a 06 ~ w o I 0 0 ~ St w
Q4 02
(I)
o
a
.
0.25
~
I
~d YH0 Dy I I I II I 030 I II I II I
Gd I
I II
I
I I
E I
I
I
I
I 035 I
I
I I I
I
Ar(A)
Fig. 2. Moles of rare earth on octahedral site in RE3[RE5 Ga2 ~]Ga3O12 versus octahedral radii difference.
degree of departure from stoichiometry for the pulled crystals, i.e., the value of x in the general formula RE3[RE~Ga2 ~]Ga3O12 by assuming the average radius on the octahedral site is a function of mole fraction: ray Ar
r~~+ 1(2—x) roa,
—
~x
=
rav—roa
=
(1) (2) (3)
~x (r~~—rrj~).
It has also been showni) that a change in the octahedral ionic radius can be related to the lattice parameter change by the following relationship: Aa0/Ar
=
1.6 15.
(4)
Combining (3) and (4), one obtains for the degree of subsitution on the octahedral site: x
=
2Aa0/l .615
(rRE
octahedral sitehypothesis, increases with decreasing ionic radius away To from test this the stoichiometric a melt 3:5 with ratio.the composition Y grown 309Ga491Oi2 from this melt was and prepared. lattice Aparameter crystal wasofthen using the technique mentioned above. The 12.2971 measured lattice i.e., slightly parameterat larger the than topits the ofthis lattice crystal parameter was the A, crystal pulled from the stoichiometric melt and results 6) for the in an x-value of 0.11. Using Geller’s data Y 3[Y~Ga2 ~}Ga3O12 system, one obtains a lattice parameter for the composition Y3[Y05, Ga1 89JGa3O12 of 12.298 A in agreement with our measured value. These results are consistent with the proposed shift of the congruent melting composition toward the rareearth rich region of the phase diagram for the rareearth gallium garnets. Furthermore, based on these results, one would predict that pulled crystals of Pr3Ga5O52 would be nearly stoichiometric and that pulled crystals of Lu3Ga 5012 would contain the largest amount of octahedral rare-earth with an x-value of approximately 0.15 0.20.
raa),
(5)
where Aa0 is the crystal lattice parameter minus the ceramic lattice parameter while CRE and roa are the ionic radii for the rare-earth and gallium ions, respectively, in octahedral coordination. The calculated values of x for each of the pulled rare-earth gallium garnets are also listed in table 1. Fig. 2 shows a plot of x versus Ar for each rare-earth galhum garnet and clearly shows that as the difference between the rare earth octahedral ionic radius and that of octahedral gallium approaches zero, the departure of
The authors would like to thank A. J. Valentino for his assistance in the crystal growth and J. W. Nielsen for his helpful discussions. References I) L. Sucho~s,M. Kokta and V. J. Flynn, J. Solid State Chem. 2 (1970) 137. 2) L. Suchow and M. Kokta, J. Solid State Chem. 5 (1972) 329. 3) S. Geller, G. P. Espinosa, L. D. Fullmer and P. B. Crandall, Mater. Res. Bull 7 (1972) 1219. 4) J. R. Carruthers, M. Kokta, R. L. Barns and M. Grasso, J. Crystal Growth 19 (1973) 204. 5) S. J. Schneider, R. S. Roth and J. L. Waring, J. Res. NatI. Bur. Std. 65a (1961) 345. 6) S. Geller, Z. Krist. 125 (1967) 1. 7) G. D. Brandle and A. J. Valentino, J. Crystal Growth 12 (1972) 3. 8) C. D. Brandle, D. C. Miller and I. W. Nielsen, I. Crystal Growth 12 (1972) 195. 9) R. L. Barns, in: Advances in X-ray Analysis, Vol. 15, Eds. Heinrich et al. (Plenum, New York, 1972) pp. 330 338. 10) R. D. Shannon and C. T. Prewitt, Acta Cryst. B 25 (1970) 925. II) K. L. Keester and G. G. Johnson, Jr., J. AppI. Cryst. 4(1971) 178.
C
North-Holland Publishing Co.
CRYSTAL STOICHIOMETRY OF CZOCHRALSKI GROWN RARE-EARTH GALLIUM GARNETS C. D. BRAN DLE* and R. L. BARNS Bell Laboratories, Murray Hill, New Jersey 07974, U.S.A. Received 18 July 1974; revised manuscript received 19 August 1974 The observed lattice parameters of Czochralski grown rare-earth gallium garnets are reported and were found to be larger than those of stoichiometric ceramic samples. The difference is attributed to some of the rare-earth ions occupying the octahedral site which results from a shift ofthe congruent melting composition toward the rare-earth rich region of the phase diagram. The degree of octahedral rare-earth substitution was found to be a function ofthe ionic radius and ranges from x 0.01 for Nd 3Ga5O12 to x 0.09 for Y3Ga,O12 in (RE3 lRE~Ga2 0]Ga30i2).
In this letter we report on the observed difference between the lattice parameters of pulled rare-earth gallium garnets and those of ceramic samples reported in the literature. We attributed this difference in lattice parameter to the rare-earth ion partially occupying the octahedral site in4)theand garnet structure’ Schneider et 3), al.5) have Carruthersnon-stoichiometric et al. examined ceramic samples of Gd 3Ga5Oi 2 and Y3Ga5O~2 respectively and concluded that there exists a solid solution range of the rare6)earth has in the garnet structure. Gellersample measured the density of aFurthermore, non-stoichiometric of Y 3 [Y0 69Ga1 3flGa3O1 23and concluded is + for Ga3 + inthat the there garnet a direct substitution of Y structure as opposed to an oxygen gallium Vacancy. All crystals were grown from stoichiometric melts, i.e., a 3:5 using mole ratio of the rare earth oxidemelts to containing gallium oxide, the growth furnace, sample pretreatment and conditions reported earlier for gadolinium gallium garnet7’8). Lattice parameters were measured at 25.0 °Cby the HPM method9) on
are used in the garnet structure, the departure of the single crystal lattice parameter from the observed powder data becomes more pronounced. Using the data in table 1 along with the literature data from ceramic samples, one can calculate the 2 ~
250
-
~ ~
2.40 230
--
~
220
2 IC
~ SINGLE CRYSTAL DATA
0
~ ‘t
0.96
1b 0.98
I
~m
.00
Y
1°
i~b I
.02
I 04
~
I
06
IONIC RADIUS
1.08
110
I
~jd
F~r
112
114
(A)
6) versus rare-earth Fig. 1. Lattice parameters of single crystals grown from stoidodecahedral ionic radius. chiometric melts and literature powder data TABLE I
Composition of garnets RE 3[RE~,Ga2 stoichiometric melts~]Ga3O12grown from
etched samples taken from the top of each of the crystals. The uncertainty (3 a) in the lattice parameter is about 0.0002 A. The results of these measurements are given in table 1 and shown graphically in fig. 1. In addition, fig. 1 shows a linear least squares fit of both the 6). single As crystal data and previous ceramic literature data can be seen from the figure, as smaller rare earth ions Present address: Union Carbide Corporation, San Diego, California 92123, U.S.A. *
169
Rare earth Nd Sm Eu Gd Tb” Dy Ho Y
r
10)
0.995 0.964 0.950 0.938 0.923 0.908 0.894 0.892
a0~(crystal)
Aa0
x
12.5090 12.4384 12.4084 12.3831 12.3486 12.3196 12.2957 12.2945
0.003 0.005 0.006 0.007
0.0l~ 0.018 0.022 0.027
0.013 0.0I4~’) 0.020
0.056 0.063 0.091
Ceramic data not available. ~ A(CuKo 1) 1.540562 A. *
170
C. D. BRANDLE AND R. L. BARNS
the crystal from stoichiometry increases. These results suggest that the solubility of the rare-earth ion in the
01 o I-
resulting in a shift ofthe congruent melting composition
08
a 06 ~ w o I 0 0 ~ St w
Q4 02
(I)
o
a
.
0.25
~
I
~d YH0 Dy I I I II I 030 I II I II I
Gd I
I II
I
I I
E I
I
I
I
I 035 I
I
I I I
I
Ar(A)
Fig. 2. Moles of rare earth on octahedral site in RE3[RE5 Ga2 ~]Ga3O12 versus octahedral radii difference.
degree of departure from stoichiometry for the pulled crystals, i.e., the value of x in the general formula RE3[RE~Ga2 ~]Ga3O12 by assuming the average radius on the octahedral site is a function of mole fraction: ray Ar
r~~+ 1(2—x) roa,
—
~x
=
rav—roa
=
(1) (2) (3)
~x (r~~—rrj~).
It has also been showni) that a change in the octahedral ionic radius can be related to the lattice parameter change by the following relationship: Aa0/Ar
=
1.6 15.
(4)
Combining (3) and (4), one obtains for the degree of subsitution on the octahedral site: x
=
2Aa0/l .615
(rRE
octahedral sitehypothesis, increases with decreasing ionic radius away To from test this the stoichiometric a melt 3:5 with ratio.the composition Y grown 309Ga491Oi2 from this melt was and prepared. lattice Aparameter crystal wasofthen using the technique mentioned above. The 12.2971 measured lattice i.e., slightly parameterat larger the than topits the ofthis lattice crystal parameter was the A, crystal pulled from the stoichiometric melt and results 6) for the in an x-value of 0.11. Using Geller’s data Y 3[Y~Ga2 ~}Ga3O12 system, one obtains a lattice parameter for the composition Y3[Y05, Ga1 89JGa3O12 of 12.298 A in agreement with our measured value. These results are consistent with the proposed shift of the congruent melting composition toward the rareearth rich region of the phase diagram for the rareearth gallium garnets. Furthermore, based on these results, one would predict that pulled crystals of Pr3Ga5O52 would be nearly stoichiometric and that pulled crystals of Lu3Ga 5012 would contain the largest amount of octahedral rare-earth with an x-value of approximately 0.15 0.20.
raa),
(5)
where Aa0 is the crystal lattice parameter minus the ceramic lattice parameter while CRE and roa are the ionic radii for the rare-earth and gallium ions, respectively, in octahedral coordination. The calculated values of x for each of the pulled rare-earth gallium garnets are also listed in table 1. Fig. 2 shows a plot of x versus Ar for each rare-earth galhum garnet and clearly shows that as the difference between the rare earth octahedral ionic radius and that of octahedral gallium approaches zero, the departure of
The authors would like to thank A. J. Valentino for his assistance in the crystal growth and J. W. Nielsen for his helpful discussions. References I) L. Sucho~s,M. Kokta and V. J. Flynn, J. Solid State Chem. 2 (1970) 137. 2) L. Suchow and M. Kokta, J. Solid State Chem. 5 (1972) 329. 3) S. Geller, G. P. Espinosa, L. D. Fullmer and P. B. Crandall, Mater. Res. Bull 7 (1972) 1219. 4) J. R. Carruthers, M. Kokta, R. L. Barns and M. Grasso, J. Crystal Growth 19 (1973) 204. 5) S. J. Schneider, R. S. Roth and J. L. Waring, J. Res. NatI. Bur. Std. 65a (1961) 345. 6) S. Geller, Z. Krist. 125 (1967) 1. 7) G. D. Brandle and A. J. Valentino, J. Crystal Growth 12 (1972) 3. 8) C. D. Brandle, D. C. Miller and I. W. Nielsen, I. Crystal Growth 12 (1972) 195. 9) R. L. Barns, in: Advances in X-ray Analysis, Vol. 15, Eds. Heinrich et al. (Plenum, New York, 1972) pp. 330 338. 10) R. D. Shannon and C. T. Prewitt, Acta Cryst. B 25 (1970) 925. II) K. L. Keester and G. G. Johnson, Jr., J. AppI. Cryst. 4(1971) 178.