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测定了单分散正八面体AgBr乳剂中加入不同量CdBr_2和KBr以后的介电吸收频谱。发现Cd~(2+)离子的表面掺杂使正八面体AgBr乳剂的介电吸收峰向低频方向位移。这种变化在CdBr_2的加入量为0—2×10~(-2)mol/mol AgBr范围内尤为明显。说明掺杂Cd~(2+)使正八面体AgBr乳剂中AgBr微晶的介电电导率σ_2显著下降。能进入AgBr微晶表面层晶格中的Cd~(2+)离子的数量不仅与乳剂中Cd~(2+)离子的浓度有关,而且与乳剂中的Br~-离子浓度有关。通过简单的水洗,可以将掺杂的Cd~(2+)大部分除去。水洗后,样品的介电吸收峰又向高频方向回移。在本实验条件下,Cd~(2+)离子掺杂的这种“可逆性”表明进入AgBr微晶中的Cd~(2+)离子主要是处在AgBr微晶的表面层内。样品介电吸收峰频率位置的这种可逆变化表明:非均匀电介质中的界面极化效应在保持连续相不变时,受分散相颗粒表面层物质的组成和结构的影响很大。
The dielectric absorption spectra of monodisperse n-octahedral AgBr emulsions with different amounts of CdBr_2 and KBr were determined. It is found that the surface doping of Cd 2+ ions shifts the dielectric absorption peak of the octahedral AgBr emulsion to the lower frequency. This change is particularly evident in the range of 0-2 × 10 -2 mol / mol AgBr for CdBr 2. It indicates that the dielectric conductivity σ_2 of AgBr microcrystal in the octahedral AgBr emulsion is significantly decreased by doping Cd 2+. The amount of Cd 2+ ions entering into the crystal lattice of AgBr surface layer is not only related to the concentration of Cd 2+ in the emulsion, but also to the concentration of Br ~ - in the emulsion. By simple washing, most of the doped Cd 2+ can be removed. After washing, the dielectric absorption peak of the sample moves back toward the high frequency again. Under the experimental conditions, the “reversibility” of Cd 2+ doping indicates that the Cd 2+ ions entering the AgBr crystallites are mainly in the surface layer of AgBr crystallites. This reversible change in the frequency location of the dielectric absorption peak of the sample indicates that the interfacial polarization effect in the non-uniform dielectric is strongly influenced by the composition and structure of the surface layer material of the dispersed phase particles while maintaining the continuous phase.