ISSN:
1573-4889
Keywords:
LEAD-IODIDE FILM
;
DOPING EFFECT
;
SHORT-CIRCUIT
;
MOTT'S ELECTRICAL FIELD
;
SCHOTTKY-WAGNER DISORDER
;
HOLE MIGRATION
;
ION TRANSPORT
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The influence of Ag as a lower-valent dopant onthe kinetics of lead iodination under normal andshort-circuit conditions in iodine pressures of 0.615 to6.578 kPa in the temperature range of 423 to 523 K was investigated. Like pure Pb, Ag-doped Pbalso follows the parabolic law of film growth. Theisothermal parabolic rate constants are found todecrease in the presence of the dopant. The iodinevapor-pressure dependence of isothermal parabolic rateconstants was observed to be kP ∝p I2 1/2 . Results for normal iodination areexplained in terms of migration of electron holes underthe influence of Cabrera-Mott's electrical field across the film. Theactivation energy for normal iodination of Ag-doped Pbis estimated to be 84 kJ•mol-1 comparedto that of 64 kJ•mol-1 for pure lead. Therate of iodide-film growth has been found to decrease further undershort-circuit mode of experiments. Such observationshave been explained with the concept of ion migration asthe ratelimiting step for the film-growth process. The iodine pressure dependence of the rateconstants under short-circuit conditions is observed tobe kP ∝ p I2 1/3 associatedwith an activation energy value of 66kJ•mol-1. Unlike pure lead, introduction of additional resistances in series to theshort-circuit Pt path during iodination of Ag-doped Pbcaused an increase in the rates with gradual increasedvalue of resistances. Kinetics results are explained by considering the prevalence ofSchottky-Wagner type of point defects in lead iodide.The driving forces for migration of the defect speciesthrough the growing pure PbI2 films andAg-doped PbI2 are confirmed to be Wagner's electrochemical potentialgradient and Cabrera-Mott's electrical field,respectively. The iodide films were characterized bySEM, EDS, EPMA, AES, and XRD analyses to substantiatethe kinetic results.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1018855129931
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