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Electrical conductivity of ammonium perchlorate
Solid State Communications ,Vol. 5,pp. 225-227,1967.
Pergamon Press Ltd. Printed in Great Britain
ELECTRICAL CONDUCTIViTY OF AMMONI1JM PERCHLORATE J. N. Maycock, V.R. Pai Verneker and C. S. Gorzynski Jr. Research Institute for Advanced Studies, Martin Company Division, 1450 South Rolling Road, Baltimore, Maryland 21227,U.S.A. (Received 13 January 1967 by H. Suhl)
Electrical conductivity measurements, using an applied d. c. potential, have been made on a single crystal of ammonium perchiorate. An interpretation of the conductivity plot has been tentatively based on the assignment of the Frenkel defect structure to the crystal in the orthorhombic form and Schottky disorder in the cubic form. Using this model ~h, the energy of migration of a defect, has been calculated to be 0. 5 eV and h, the energy for the formation of a defect pair, to be 0. 6 and 3. 0 eV respectively.
THE ELECTRICAL conductivity studies of ionic solids have been almost completely done with respect to thermally stable salts such as the alkali halides, alkaline earth halides and silver halIdes. 1 The only studies of metastable materials, such as azides and perchiorates, have been performed respectively by Jacobs and Tompkins and by Freeman. ~ Unfortunately these electrical conductivity studies have been made on pressed pellets rather than on the more desirable system of single crystals.
Then the electrical conductivity would be measured. The physical dimensions of the crystal were measured before and after a run and were found to vary by approx. 1%. A typical plot of aT vs. l/T is shown In Fig. 1. It is very apparent that this curve is composed of four linear regions distinguished in Fig. 1 by the lettering system. The respective activation energies are displayed below in Table 1, and the “knees” are at 255, 171 and 92°C.
In this communication we are reporting electrical conductivity measurements made on single crystal parallelopipeds of ammonium perchlorate grown from an aqueous solution. Typical a,b,c dimensions would be 5, 5 and 3mm. The. actual measurements were made by applying a d. c. voltage to the crystal, maximum used was 40 volts, and measuring the current with a Cary Vibrating Reed electrometer fitted with a multiple resistor turret head. The temperature control was accurate to ± 0. 5°C, and the crystal temperature was measured by a second thermocouple in close proximity to the platinum foil electrodes. All measurements were taken with increasing temperature such that typically the furnace temperature would be raised to the desired temperature and maintained at that temperature for about 5 mm. to allow the point defect concentration of the crystal to come to equilibrium, 225
TABLE I Activation energies (eV) for conduction ____________________________________________ Range
Energy(eV)
AB
1 98
BC CD
0. 81 0 54
DE
0. 18
It was also observed that the crystals exhibited polarization effects in the temperature range, room temperature to about 125°C. Above this temperature the polarization was absent.
226
ELECTRICAL CONDUCTIVITY OF AMMONIUM PERCHLORATE
treatment, but without being subjected to an electrical field, and were found to be completely opaque after the temperature cycling. This effect is shown diagramatically in Fig. 2.
_______________________________
A
8.0
-
I— b
a’
0 -J
c ib.o-
HO-
D E
-
I
I
2.0
I
3/TK 2.4 ~0
Vol.5, No. 4
I
I
2.8
3.2
FIG. I
Plot of the electrical conductivity, a, of ammonium perchiorate as a function of temperature.
An ideal conductivity curve for a solid would be expected to show both surface and bulk conduction effects. Due to the very low activation energy associated with the region DE we tentatively speculate that the conduction observed in this region may be due to some unknown surface conduction mechanism. The crystal structure of the ammonium perchiorate prior to the studies is orthorhombic but at about 250°C changes to cubic. We are thus speculating that the region CD is the extrinsic conductivity region for the orthorhombic form. Using this interpretation we have calculated that L~h,the energy for migration of a defect, is 0.5 eV and h1, the energy required for the formation of defect pair, is 0.6 eV. This low value for h1 leads us to speculate that the defect structure is of the Frenkel defects is usually of the order of 1.0Frenkel eV. type since h for systems exhibiting The “knee” at 255°Cis undoubtedly due to the change in crystal structure. Assuming that the crystal is intrinsic in the range BC then we expectthere that it will also be intrinsic in ABstructalthough has been a change of crystal ure. Using the same value for t~h,it is found that h 1 in AB is now approx. 3.0 eV. Such a high value would predict that the defect structure in this range is of the Schottky form. The observed polarization effects are obviously due to a build-up of ions at the elect-
__________
I
I
(
-
A
B FIG. 2
A diagramatic representation of the crystals alter being heated to 3 00°C and cooled down to room temperature, A, with an applied voltage and B with no applied voltage, Upon removal of the crystal from the conductivity cell It was very apparent that the crystal surface near the positive electrode had become opaque whilst the remainder of the crystal was still in its original transparent state. Other crystals were subjected to the same temperature
rodes the temperature with very little rangeleakage where polarization or destruction. effects In are absent the implication is that the carriers are destroyed. This is qualitatively what one may expect perchlorate since the thermal of ammonium is onlydecomposition noticeable above 150°C. The reason for the excessive decomposition at the positive electrode could be due to a preponderance of C10 ions at that electrode. This in turn implies greater decomijositton since it is believed that the C1O ion dominates the decomposition. Acknowledgement We would like to thank Mr. E. E. Hackman of Thiokol Corp., Elkton, Maryland for supplying the single crystals of ammonium perchiorate. -
Vol.5, No.4
ELECTRICAL CONDUCTIVITY OF AMMONIU?vL PERCHLORATE References
1.
LIDIARD A.B., Handb.Physik. 20, 246 (1957).
2.
JACOBS P. W. M. and TOMPKINS F. C., J. Chem. Phys. 23, 1445 (1955).
3.
FREEMAN E.S., Nature, 199,1280 (1963).
An einem einzelnen Ammonium Perchiorate Kristall wurden elektrlsche Leitungsf~higkeitsMessungen ausgefUhrt mlttels einem angewantem d. c. potential. Als basis zur Auswertung der Leltungsf~.higkeits Kurve wurde die Freneki Lücken-struktur zum-Kristall in der orthorhoristie Form und die Schottky Lückenstruktur in der kublschen Form angewant. Bel der Anwendung dieses Modelles A H, wurde die Energie der Migration einer Ltlcke mIt 0,5 eV bestimmt and h, die Energie fir die Formation eines LUcken-Paares, ist 0,6 resp. 3,0 eV.
227
Pergamon Press Ltd. Printed in Great Britain
ELECTRICAL CONDUCTIViTY OF AMMONI1JM PERCHLORATE J. N. Maycock, V.R. Pai Verneker and C. S. Gorzynski Jr. Research Institute for Advanced Studies, Martin Company Division, 1450 South Rolling Road, Baltimore, Maryland 21227,U.S.A. (Received 13 January 1967 by H. Suhl)
Electrical conductivity measurements, using an applied d. c. potential, have been made on a single crystal of ammonium perchiorate. An interpretation of the conductivity plot has been tentatively based on the assignment of the Frenkel defect structure to the crystal in the orthorhombic form and Schottky disorder in the cubic form. Using this model ~h, the energy of migration of a defect, has been calculated to be 0. 5 eV and h, the energy for the formation of a defect pair, to be 0. 6 and 3. 0 eV respectively.
THE ELECTRICAL conductivity studies of ionic solids have been almost completely done with respect to thermally stable salts such as the alkali halides, alkaline earth halides and silver halIdes. 1 The only studies of metastable materials, such as azides and perchiorates, have been performed respectively by Jacobs and Tompkins and by Freeman. ~ Unfortunately these electrical conductivity studies have been made on pressed pellets rather than on the more desirable system of single crystals.
Then the electrical conductivity would be measured. The physical dimensions of the crystal were measured before and after a run and were found to vary by approx. 1%. A typical plot of aT vs. l/T is shown In Fig. 1. It is very apparent that this curve is composed of four linear regions distinguished in Fig. 1 by the lettering system. The respective activation energies are displayed below in Table 1, and the “knees” are at 255, 171 and 92°C.
In this communication we are reporting electrical conductivity measurements made on single crystal parallelopipeds of ammonium perchlorate grown from an aqueous solution. Typical a,b,c dimensions would be 5, 5 and 3mm. The. actual measurements were made by applying a d. c. voltage to the crystal, maximum used was 40 volts, and measuring the current with a Cary Vibrating Reed electrometer fitted with a multiple resistor turret head. The temperature control was accurate to ± 0. 5°C, and the crystal temperature was measured by a second thermocouple in close proximity to the platinum foil electrodes. All measurements were taken with increasing temperature such that typically the furnace temperature would be raised to the desired temperature and maintained at that temperature for about 5 mm. to allow the point defect concentration of the crystal to come to equilibrium, 225
TABLE I Activation energies (eV) for conduction ____________________________________________ Range
Energy(eV)
AB
1 98
BC CD
0. 81 0 54
DE
0. 18
It was also observed that the crystals exhibited polarization effects in the temperature range, room temperature to about 125°C. Above this temperature the polarization was absent.
226
ELECTRICAL CONDUCTIVITY OF AMMONIUM PERCHLORATE
treatment, but without being subjected to an electrical field, and were found to be completely opaque after the temperature cycling. This effect is shown diagramatically in Fig. 2.
_______________________________
A
8.0
-
I— b
a’
0 -J
c ib.o-
HO-
D E
-
I
I
2.0
I
3/TK 2.4 ~0
Vol.5, No. 4
I
I
2.8
3.2
FIG. I
Plot of the electrical conductivity, a, of ammonium perchiorate as a function of temperature.
An ideal conductivity curve for a solid would be expected to show both surface and bulk conduction effects. Due to the very low activation energy associated with the region DE we tentatively speculate that the conduction observed in this region may be due to some unknown surface conduction mechanism. The crystal structure of the ammonium perchiorate prior to the studies is orthorhombic but at about 250°C changes to cubic. We are thus speculating that the region CD is the extrinsic conductivity region for the orthorhombic form. Using this interpretation we have calculated that L~h,the energy for migration of a defect, is 0.5 eV and h1, the energy required for the formation of defect pair, is 0.6 eV. This low value for h1 leads us to speculate that the defect structure is of the Frenkel defects is usually of the order of 1.0Frenkel eV. type since h for systems exhibiting The “knee” at 255°Cis undoubtedly due to the change in crystal structure. Assuming that the crystal is intrinsic in the range BC then we expectthere that it will also be intrinsic in ABstructalthough has been a change of crystal ure. Using the same value for t~h,it is found that h 1 in AB is now approx. 3.0 eV. Such a high value would predict that the defect structure in this range is of the Schottky form. The observed polarization effects are obviously due to a build-up of ions at the elect-
__________
I
I
(
-
A
B FIG. 2
A diagramatic representation of the crystals alter being heated to 3 00°C and cooled down to room temperature, A, with an applied voltage and B with no applied voltage, Upon removal of the crystal from the conductivity cell It was very apparent that the crystal surface near the positive electrode had become opaque whilst the remainder of the crystal was still in its original transparent state. Other crystals were subjected to the same temperature
rodes the temperature with very little rangeleakage where polarization or destruction. effects In are absent the implication is that the carriers are destroyed. This is qualitatively what one may expect perchlorate since the thermal of ammonium is onlydecomposition noticeable above 150°C. The reason for the excessive decomposition at the positive electrode could be due to a preponderance of C10 ions at that electrode. This in turn implies greater decomijositton since it is believed that the C1O ion dominates the decomposition. Acknowledgement We would like to thank Mr. E. E. Hackman of Thiokol Corp., Elkton, Maryland for supplying the single crystals of ammonium perchiorate. -
Vol.5, No.4
ELECTRICAL CONDUCTIVITY OF AMMONIU?vL PERCHLORATE References
1.
LIDIARD A.B., Handb.Physik. 20, 246 (1957).
2.
JACOBS P. W. M. and TOMPKINS F. C., J. Chem. Phys. 23, 1445 (1955).
3.
FREEMAN E.S., Nature, 199,1280 (1963).
An einem einzelnen Ammonium Perchiorate Kristall wurden elektrlsche Leitungsf~higkeitsMessungen ausgefUhrt mlttels einem angewantem d. c. potential. Als basis zur Auswertung der Leltungsf~.higkeits Kurve wurde die Freneki Lücken-struktur zum-Kristall in der orthorhoristie Form und die Schottky Lückenstruktur in der kublschen Form angewant. Bel der Anwendung dieses Modelles A H, wurde die Energie der Migration einer Ltlcke mIt 0,5 eV bestimmt and h, die Energie fir die Formation eines LUcken-Paares, ist 0,6 resp. 3,0 eV.
227