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Crystal growth and properties of the lead phosphate Pb5P4O15
Mat. Res. Bull. Vol. 7, pp. 883-890, 1972. Pergamon Press, Inc. Printed in the United States.
CRYSTAL GROWTH AND PROPERTIES OF THE LEAD PHOSPHATE PbsP4015
L. H. Brixner, P. E. Bierstedt, and Co M. Foris Central Research Department* E. I. du Pont de Nemours and Company Wilmington, Delaware 19898
(Received June 22, 1972; Refereed)
ABSTRACT Single crystals of PbgP4015 have been grown by the Czochralski technique. ~t robm temperature the compound has the monoclinic space group P21/c with lattice parameters a = 12.405 ~, b = 18.441 A, c = 24.752 ~, ~ = 92.26 ° , Z = 16. A structural phase transformation has been observed at 250°C. Dielectric properties of this compound have been measured and are discussed.
Introduction In a recent paper (i) we have described crystal growth and space group determination for the lead pyrophosphate
Pb2P207 .
This information was consistent with earlier studies by Argyle and Hummel
(2) who had shown that in the PbO/P205
least seven different lead phosphates
exist.
system at
The space group and
structure of most of these compounds remain to be solved; only Pb3(P04) 2, lead orthophosphate, terized structurally by Keppler
(3).
to date
has been completely characThis paper is part of a
continuing effort to obtain more detailed information on the great variety of lead phosphates.
*Contribution No. 1944 883
884
LEAD
PHOSPHATE
Vol. 7, No. 9
Experimental Feed Preparation and Crystal Growth PbsP4015 feed material was prepared by interacting PbCO 3 (Fisher Scientific Co., certified) and (NH4)H2PO 4 (BDH Chemicals, Ltd., England, analytical grade) according to: 4(NH4)~P04
+ 5PbC03
~ PbsP#015 + 4 N ~
+ 6H20 + 5C02
first at 300°C for i0 to 14 hrs and after homogenization in a second firing step at 700°C for another 4-6 hrs.
About 250 g of
the pure white product was melted in a 50-ml Pt crucible by means of rf heating,
using an ECC0 20 KVA power generator.
The com-
pound melted congruently at 920°C (determined by uncorrected optical pyrometry) with no noticeable vapor pressure. initiated on a platinum wire, rotated at i0 rpm. generally was 0.5 to 0.8 cm/hr.
Growth was The growth rate
Immediately after termination of
crystal growth, the crystal was pulled into an anneal furnace held at 700°C. hr.
It was then cooled at a programed rate of 40°C/
Quite frequently the glass-clear colorless crystal cracked
into smaller fragments, electrical studies.
large enough however, for optical and
Chemical analysis of the single crystal gave
73.2% Pb and 9.0% P in good agreement with the theoretical amounts of 74.00 and 8.85%,
respectively.
X-Ray Stud[, Single crystal photographs were taken with a precession camera using Mo radiation.
X-ray powder patterns were obtained
at 25°C with a Guinier-H~gg camera with both Cu radiation using an internal standard of KC1 (a = 6.2931 ~) and with Cr radiation using an internal standard of Co203 (a = 8°0832 ~).
Refined cell
dimensions were obtained by a least squares treatment of the Guinier data. Dielectric Measurements The dielectric measurements were carried out on a single crystal plate as a function of temperature from 25 ° to 300°C at a
V ol. 7, No. 9
LEAD PHOSPHATE
frequency of 105 Hz.
885
Gold electrodes were sputtered onto the
sample faces and guarded two-terminal capacitance (C) and dissipation factor (tan D) measurements were made with a HewlettPackard Model 4270A automatic capacitance bridge.
The digital
output signals of this bridge were converted to analog information and displayed on x-y recorders.
The x-axes of the recorders
displayed the sample temperature as monitored by a chromel-alumel thermocouple. Results and Discussion The lattice parameters determined by least squares refinement for both types of radiation are summarized in Table 1. All observations were indexed for both Cu and Cr radiation (96 in the former and 72 in the latter case).
The reason for the use
of Cr radiation was to observe the line splitting, which could just barely be detected with Cu radiation, in a more pronounced manner.
The pyrometrically determined density was 6.507 g.m1-1. TABLE 1 Lattice Parameters and Space Group of Pb5P4015
Radiation
a, ~
b, ~
c, ~
~, dg
V, ~3
Space Group
Cu
12.405+__1 18.#41+__1 2#.752+__2 92.26+__1 5657.8+__5 P21/c
Cr
12.399+_1
18.#52+_1
24.755+_1
92.29+_1
5659.5+--6 P21/c
Based on this value, the number of molecules per unit cell Z : 16 and the calculated x-ray density is 6.573 g.ml -I.
The single
crystal photographs indicated an orthorhombic subcell with dimensions : a =
8.58
b =
8.92
c = 18.36 The relationship between the monoclinic cell and the orthorhombic subcell is shown in Fig. 1.
This may be representative of the
886
LEAD PHOSPHATE
'j
Vol. 7, No. 9
/
b (o)
FIG. i Monoclinic Cell with 0rthorhombic Subcell high-temperature structure, as this compound, unlike Pb2P207, undergoes a phase transition at 251°C.
This temperature was
established by differential scanning calorimetry, using a chrome~ alumel thermocouple and a heating rate of 15°C/min. verified by a dielectric anomaly near 250°C.
It was also
The melting point
of 949°C was measured at a heating rate of 10°C/min with a Du Pont 900 thermal analyzer, employing a Pt/Pt 13% Rh thermocouple.
The only high temperature x-ray information available at
present is a diffractometer pattern at 300°C showing a definite change in symmetry.
We can therefore only assume that PbsP4015
is orthorhombic above 250°C based on the above-mentioned subcell observations.
It is of particular interest to note that Argyle
and Hummel (2) observed a "thermal inversion or discontinuity" when running thermal-expansion curves.
For PbsP4015 this inver-
sion was observed at about 300°C, which is not too far from our observed transformation temperature.
This suggests that the
V o l . 7, No. 9
LEAD PHOSPHATE
887
TABLE 2 Observed and Calculated d-Spaclngs for PbsP4015
HKL
I**
D(OBS)**
020 -112 -200 210 024 -132 -133 -204 230 204 214 016 -302 224 -312 312 116 215 313 242 -314 -331 -332 -136 332 136 -244 250 400 008 340 2D2 061 -342 -161 -316 254 -237
5 5 5 20 i0 l0 20 20 50 5 35 55 i0 70 75 20 25 2 i0 85 5 50 95 90 90 90 i00 55 65 65 55 45 40 60 65 20 15 50
9.2388 8.0456 6.1963 5.8740 5.1389 5.0651 4.6140 4.4672 4.3633 4.2947 4.1813 4.0219 3.9656 3.8886 3.8761 3.7924 3.7850 3.7204 3.5689 3.5209 3.4472 3.4120 3.3329 3.3285 3.2788 3.2737 3.2094 3.1699 3.0973 3.0909 3.0764 3.0551 3.0496 3.0060 2.9649 2.9394 2.7983 2.7838
D(OBS)*
I*
5.87
8
4.60 4.46 4.35 4.29 4.17 4.00
16 ll 19 7 27 21
3.87 3.79
64 20
3.52
48
3.40 3.33
ii 77
3.27
77
3.20 3.16
56 49
3.07
i00
3.00
2.78
35
27
D(CALC) 9.2210 8,0384 6.1969 5.8741 5.1352 5.0638 4.6168 4.4657 4.3642 4.2930 4.1812 4.0226 3.9656 3.8919 3.8770 3.7901 3.7836 3.7157 3.5677 3.5212 3.4379 3.4116 3.3324 3.3280 3.2767 3.2725 3.2077 3.1694 3.0984 3.0913 3.0767 3.0554 3.0502 3.0065 2.9651 2.9391 2.7976 2.7840
HKL
I**
D(OBS) ~
-218 351 208 -164 432 352 327 -346 270 166 -266 364 532 -372 540 068 -506 280 -516 408 1410 516 177 600 0012 464 -612 620 -381 470 -457 536 3310 630 -3410 631 -474
50 55 50 30 i0 15 15 15 lO 15 l0 i0 i0 50 45 40 20 20 20 20 15 50 50 5 5 60 60 15 20 15 20 60 55 15 i0 15 45
2.7799 2.7264 2.7238 2.6959 2.6803 2.6703 2.5325 2.5006 2.4252 2.4051 2.3069 2.2730 2.2460 2.1947 2.1827 2.1795 2.1622 2.1604 2.1478 2.1461 2.1342 2.0748 2.0735 2.0658 2.0610 2.0399 2.0380 2.0155 2.0094 2.0064 1.9983 1.9769 1.9754 1.9580 1.9555 1.9463 1.9239
D(OBS)*
I*
2.72
60
2.69
33
2.53 2.49
5 5
2.18
33
2.11
13
2.07
49
2.04
39
2.01
13
1.97
53
1.945 1.92
5 13
D(CALC) 2.7788 2,7266 2.7237 2.6969 2.6800 2.6709 2.5329 2.5010 2.4245 2.4059 2.3084 2.2722 2.2454 2.1944 2.1832 2.1796 2.1622 2.1606 2.1475 2.1465 2.1338 2.0749 2.0739 2.0656 2.0609 2.0400 2.0380 2.0156 2.0095 2.0071 1.9976 1.9772 1.9754 1.9580 1.9558 1.9462 1.9235
*Argyle and Hummel, J. Am. Ceram. Soc. 43, 452 (1960). **This work
expansion anomaly at this point is caused by a structural rearrangement.
The preliminary x-ray data by Argyle and Hummel
(2) are also in good agreement with our d-spacings as can be seen in Table 2.
While Argyle and Hummel (2) missed many of the
weaker reflections,
the agreement is quite good even with regard
888
LEAD PHOSPHATE
to the intensities.
Vol. 7, No. 9
It should also be pointed out that the
listed intensities are those obtained from strongly overexposed Guinier patterns and therefore exaggerate the absolute values. Although the space group determination was unique and suggested centrosymmetry for Pb5P4015, we did run a second harmonic generation test in equipment similar to that described by Perry and Kurtz (4).
This test was negative, supporting the centric 2/m
point group.
The refractive index of PbsP#015 was found to be
1.92. In contrast to Pb2P207 and Pb3(P0#)2, the present lead phosphate shows no tendency to cleave into sheets. As the difference between PbsP~015 and Pb6P4016[Pb3(P04)2] is only 1 mole PbO, it would be of interest to establish the structure of the first compound in greater detail to determine its relationship to the orthophosphate whose structure is completely solved. Our dielectric measurements on a (010) oriented plate show that single crystalline Pb5P4015 has a room-temperature dielectric constant (K') of 30 and a tan 5 of .001.
50
'
I
'
I
,
I IO0
~
I 2OO
The K' in-
'
40-
KI
3020I00
3OO
TE M PERATU RE, °C FIG.
2
Dielectric Constant vs. Temperature for PbsP4015
Vol. 7, No. 9
LEAD
PHOSPHATE
889
creases slowly with temperature and exhibits a small step anomaly near 250°C.
This behavior is shown in Fig. 2.
With the present
high sensitivity dielectric techniques, we find such measurements very helpful in establishing the dielectric anomalies associated with phase transitions, even on polycrystalline specimens.
In
fact, low-energy phase transitions can be detected by this technique in those instances where DSC methods fail, since the heating or cooling rate is not a critical factor in the detection of the transition. Acknowledgment s The authors wish to thank Dr. J. D. Bierlein for running the second harmonic generation test and determining the refractive index. References 1.
L. H. Brixner, P. E. Bierstedt and C. M. Foris, J. Solid State Chem., in print.
2.
J. F. Argyle and F. A. Hummel, J. Amer. Ceram. Soc. 43, 452 (1960).
3.
V. Keppler, Z. Kristallogr. 132, 228 (1970).
4.
R. J. Blume, Rev. Sci. Instr. 32, 598 (1961).
5.
S. K. Perry and T. T. Kurtz, J. Appl. Phys. 39, 3798 (1968).
CRYSTAL GROWTH AND PROPERTIES OF THE LEAD PHOSPHATE PbsP4015
L. H. Brixner, P. E. Bierstedt, and Co M. Foris Central Research Department* E. I. du Pont de Nemours and Company Wilmington, Delaware 19898
(Received June 22, 1972; Refereed)
ABSTRACT Single crystals of PbgP4015 have been grown by the Czochralski technique. ~t robm temperature the compound has the monoclinic space group P21/c with lattice parameters a = 12.405 ~, b = 18.441 A, c = 24.752 ~, ~ = 92.26 ° , Z = 16. A structural phase transformation has been observed at 250°C. Dielectric properties of this compound have been measured and are discussed.
Introduction In a recent paper (i) we have described crystal growth and space group determination for the lead pyrophosphate
Pb2P207 .
This information was consistent with earlier studies by Argyle and Hummel
(2) who had shown that in the PbO/P205
least seven different lead phosphates
exist.
system at
The space group and
structure of most of these compounds remain to be solved; only Pb3(P04) 2, lead orthophosphate, terized structurally by Keppler
(3).
to date
has been completely characThis paper is part of a
continuing effort to obtain more detailed information on the great variety of lead phosphates.
*Contribution No. 1944 883
884
LEAD
PHOSPHATE
Vol. 7, No. 9
Experimental Feed Preparation and Crystal Growth PbsP4015 feed material was prepared by interacting PbCO 3 (Fisher Scientific Co., certified) and (NH4)H2PO 4 (BDH Chemicals, Ltd., England, analytical grade) according to: 4(NH4)~P04
+ 5PbC03
~ PbsP#015 + 4 N ~
+ 6H20 + 5C02
first at 300°C for i0 to 14 hrs and after homogenization in a second firing step at 700°C for another 4-6 hrs.
About 250 g of
the pure white product was melted in a 50-ml Pt crucible by means of rf heating,
using an ECC0 20 KVA power generator.
The com-
pound melted congruently at 920°C (determined by uncorrected optical pyrometry) with no noticeable vapor pressure. initiated on a platinum wire, rotated at i0 rpm. generally was 0.5 to 0.8 cm/hr.
Growth was The growth rate
Immediately after termination of
crystal growth, the crystal was pulled into an anneal furnace held at 700°C. hr.
It was then cooled at a programed rate of 40°C/
Quite frequently the glass-clear colorless crystal cracked
into smaller fragments, electrical studies.
large enough however, for optical and
Chemical analysis of the single crystal gave
73.2% Pb and 9.0% P in good agreement with the theoretical amounts of 74.00 and 8.85%,
respectively.
X-Ray Stud[, Single crystal photographs were taken with a precession camera using Mo radiation.
X-ray powder patterns were obtained
at 25°C with a Guinier-H~gg camera with both Cu radiation using an internal standard of KC1 (a = 6.2931 ~) and with Cr radiation using an internal standard of Co203 (a = 8°0832 ~).
Refined cell
dimensions were obtained by a least squares treatment of the Guinier data. Dielectric Measurements The dielectric measurements were carried out on a single crystal plate as a function of temperature from 25 ° to 300°C at a
V ol. 7, No. 9
LEAD PHOSPHATE
frequency of 105 Hz.
885
Gold electrodes were sputtered onto the
sample faces and guarded two-terminal capacitance (C) and dissipation factor (tan D) measurements were made with a HewlettPackard Model 4270A automatic capacitance bridge.
The digital
output signals of this bridge were converted to analog information and displayed on x-y recorders.
The x-axes of the recorders
displayed the sample temperature as monitored by a chromel-alumel thermocouple. Results and Discussion The lattice parameters determined by least squares refinement for both types of radiation are summarized in Table 1. All observations were indexed for both Cu and Cr radiation (96 in the former and 72 in the latter case).
The reason for the use
of Cr radiation was to observe the line splitting, which could just barely be detected with Cu radiation, in a more pronounced manner.
The pyrometrically determined density was 6.507 g.m1-1. TABLE 1 Lattice Parameters and Space Group of Pb5P4015
Radiation
a, ~
b, ~
c, ~
~, dg
V, ~3
Space Group
Cu
12.405+__1 18.#41+__1 2#.752+__2 92.26+__1 5657.8+__5 P21/c
Cr
12.399+_1
18.#52+_1
24.755+_1
92.29+_1
5659.5+--6 P21/c
Based on this value, the number of molecules per unit cell Z : 16 and the calculated x-ray density is 6.573 g.ml -I.
The single
crystal photographs indicated an orthorhombic subcell with dimensions : a =
8.58
b =
8.92
c = 18.36 The relationship between the monoclinic cell and the orthorhombic subcell is shown in Fig. 1.
This may be representative of the
886
LEAD PHOSPHATE
'j
Vol. 7, No. 9
/
b (o)
FIG. i Monoclinic Cell with 0rthorhombic Subcell high-temperature structure, as this compound, unlike Pb2P207, undergoes a phase transition at 251°C.
This temperature was
established by differential scanning calorimetry, using a chrome~ alumel thermocouple and a heating rate of 15°C/min. verified by a dielectric anomaly near 250°C.
It was also
The melting point
of 949°C was measured at a heating rate of 10°C/min with a Du Pont 900 thermal analyzer, employing a Pt/Pt 13% Rh thermocouple.
The only high temperature x-ray information available at
present is a diffractometer pattern at 300°C showing a definite change in symmetry.
We can therefore only assume that PbsP4015
is orthorhombic above 250°C based on the above-mentioned subcell observations.
It is of particular interest to note that Argyle
and Hummel (2) observed a "thermal inversion or discontinuity" when running thermal-expansion curves.
For PbsP4015 this inver-
sion was observed at about 300°C, which is not too far from our observed transformation temperature.
This suggests that the
V o l . 7, No. 9
LEAD PHOSPHATE
887
TABLE 2 Observed and Calculated d-Spaclngs for PbsP4015
HKL
I**
D(OBS)**
020 -112 -200 210 024 -132 -133 -204 230 204 214 016 -302 224 -312 312 116 215 313 242 -314 -331 -332 -136 332 136 -244 250 400 008 340 2D2 061 -342 -161 -316 254 -237
5 5 5 20 i0 l0 20 20 50 5 35 55 i0 70 75 20 25 2 i0 85 5 50 95 90 90 90 i00 55 65 65 55 45 40 60 65 20 15 50
9.2388 8.0456 6.1963 5.8740 5.1389 5.0651 4.6140 4.4672 4.3633 4.2947 4.1813 4.0219 3.9656 3.8886 3.8761 3.7924 3.7850 3.7204 3.5689 3.5209 3.4472 3.4120 3.3329 3.3285 3.2788 3.2737 3.2094 3.1699 3.0973 3.0909 3.0764 3.0551 3.0496 3.0060 2.9649 2.9394 2.7983 2.7838
D(OBS)*
I*
5.87
8
4.60 4.46 4.35 4.29 4.17 4.00
16 ll 19 7 27 21
3.87 3.79
64 20
3.52
48
3.40 3.33
ii 77
3.27
77
3.20 3.16
56 49
3.07
i00
3.00
2.78
35
27
D(CALC) 9.2210 8,0384 6.1969 5.8741 5.1352 5.0638 4.6168 4.4657 4.3642 4.2930 4.1812 4.0226 3.9656 3.8919 3.8770 3.7901 3.7836 3.7157 3.5677 3.5212 3.4379 3.4116 3.3324 3.3280 3.2767 3.2725 3.2077 3.1694 3.0984 3.0913 3.0767 3.0554 3.0502 3.0065 2.9651 2.9391 2.7976 2.7840
HKL
I**
D(OBS) ~
-218 351 208 -164 432 352 327 -346 270 166 -266 364 532 -372 540 068 -506 280 -516 408 1410 516 177 600 0012 464 -612 620 -381 470 -457 536 3310 630 -3410 631 -474
50 55 50 30 i0 15 15 15 lO 15 l0 i0 i0 50 45 40 20 20 20 20 15 50 50 5 5 60 60 15 20 15 20 60 55 15 i0 15 45
2.7799 2.7264 2.7238 2.6959 2.6803 2.6703 2.5325 2.5006 2.4252 2.4051 2.3069 2.2730 2.2460 2.1947 2.1827 2.1795 2.1622 2.1604 2.1478 2.1461 2.1342 2.0748 2.0735 2.0658 2.0610 2.0399 2.0380 2.0155 2.0094 2.0064 1.9983 1.9769 1.9754 1.9580 1.9555 1.9463 1.9239
D(OBS)*
I*
2.72
60
2.69
33
2.53 2.49
5 5
2.18
33
2.11
13
2.07
49
2.04
39
2.01
13
1.97
53
1.945 1.92
5 13
D(CALC) 2.7788 2,7266 2.7237 2.6969 2.6800 2.6709 2.5329 2.5010 2.4245 2.4059 2.3084 2.2722 2.2454 2.1944 2.1832 2.1796 2.1622 2.1606 2.1475 2.1465 2.1338 2.0749 2.0739 2.0656 2.0609 2.0400 2.0380 2.0156 2.0095 2.0071 1.9976 1.9772 1.9754 1.9580 1.9558 1.9462 1.9235
*Argyle and Hummel, J. Am. Ceram. Soc. 43, 452 (1960). **This work
expansion anomaly at this point is caused by a structural rearrangement.
The preliminary x-ray data by Argyle and Hummel
(2) are also in good agreement with our d-spacings as can be seen in Table 2.
While Argyle and Hummel (2) missed many of the
weaker reflections,
the agreement is quite good even with regard
888
LEAD PHOSPHATE
to the intensities.
Vol. 7, No. 9
It should also be pointed out that the
listed intensities are those obtained from strongly overexposed Guinier patterns and therefore exaggerate the absolute values. Although the space group determination was unique and suggested centrosymmetry for Pb5P4015, we did run a second harmonic generation test in equipment similar to that described by Perry and Kurtz (4).
This test was negative, supporting the centric 2/m
point group.
The refractive index of PbsP#015 was found to be
1.92. In contrast to Pb2P207 and Pb3(P0#)2, the present lead phosphate shows no tendency to cleave into sheets. As the difference between PbsP~015 and Pb6P4016[Pb3(P04)2] is only 1 mole PbO, it would be of interest to establish the structure of the first compound in greater detail to determine its relationship to the orthophosphate whose structure is completely solved. Our dielectric measurements on a (010) oriented plate show that single crystalline Pb5P4015 has a room-temperature dielectric constant (K') of 30 and a tan 5 of .001.
50
'
I
'
I
,
I IO0
~
I 2OO
The K' in-
'
40-
KI
3020I00
3OO
TE M PERATU RE, °C FIG.
2
Dielectric Constant vs. Temperature for PbsP4015
Vol. 7, No. 9
LEAD
PHOSPHATE
889
creases slowly with temperature and exhibits a small step anomaly near 250°C.
This behavior is shown in Fig. 2.
With the present
high sensitivity dielectric techniques, we find such measurements very helpful in establishing the dielectric anomalies associated with phase transitions, even on polycrystalline specimens.
In
fact, low-energy phase transitions can be detected by this technique in those instances where DSC methods fail, since the heating or cooling rate is not a critical factor in the detection of the transition. Acknowledgment s The authors wish to thank Dr. J. D. Bierlein for running the second harmonic generation test and determining the refractive index. References 1.
L. H. Brixner, P. E. Bierstedt and C. M. Foris, J. Solid State Chem., in print.
2.
J. F. Argyle and F. A. Hummel, J. Amer. Ceram. Soc. 43, 452 (1960).
3.
V. Keppler, Z. Kristallogr. 132, 228 (1970).
4.
R. J. Blume, Rev. Sci. Instr. 32, 598 (1961).
5.
S. K. Perry and T. T. Kurtz, J. Appl. Phys. 39, 3798 (1968).