Anomalous dispersion effects, anharmonic thermal vibrations and bonding charges in indium antimonide

Abstract

Upon the inclusion of dispersion corrections in the structure factor expressions for the ZnS structure, Friedel's law is violated for all odd and all even index reflections due to bonding effects in the low angle regions and anharmonicity in the high angle regions in this type of crystals. Systematic and precise X-ray diffraction intensity measurements were carried out using a spherical single crystal of indium antimonide at 300 K. From the least squares refinement of the experimental data we obtain the Debye-Waller factors for indium and antimony as B(In) = 1.432(0.003) A ̊ 2 and B(Sb) = 0.865(0.002) A ̊ 2 with the residual index R = 2.24%. A search for anharmonic thermal vibrations was made for the present experimental data. On including the individual anharmonic thermal factors in the refinement process we obtain the anharmonic thermal parameters for indium and antimony as β(In) = −0.57(0.34) 10 −16 J A ̊ −3 and β(Sb)= −2.21(1.18) 10 −16 J A ̊ −3 , the Debye-Waller factors for the anharmonic model being B(In) = 1.333(0.003) A ̊ 2 and B(Sb) = 0.886(0.002) A ̊ 2 with R = 2.22%. The present work reveals excellent agreement, both in sign and magnitude, with the Bijvoet inequalities for a large number of reflections. In the ZnS structure, the weak quasi-forbidden reflections ( h + k + l = 4 n + 2) contain information about the covalent bond charges which was also deduced using a few 4 n + 2 type reflections. A net transfer of charge from In to Sb is observed in the present work.