Tetrahedral Ferric Complexes in Silver Halides

摘要

Single crystals of AgCl and AgBr which contained iron impurity in the ferrous state were annealed in chlorine and bromine gas at about 350C for approximately one half hour. An investigation by e.s.r. methods, after quenching to room temperature, showed that a portion of the iron impurity was oxidised to the ferric state. The stability of the ferric state at room temperature is dependent on the dislocation content of the crystals. It is suggested that the ferric ions are present interstitially in the crystal forming a complex which may be described as (FeX4)- where X is a halogen; the model in the case of AgCl requires association of the ferric ion with four nearest neighbour silver ion vacancies. (Author)