I think expansion of the cube happens as a result of doping

you might have a look at: S. Furukawa et al., Phys. Rev. B. 38, 5726 (1988)

pls send the paper @ Eric Barbagiovanni

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.38.5726

Doped hexagonal phase CdS thin film was prepared by the doping of A Cu^2. . The lattice constant decrease with the increase of Cu content. The decrease of the lattice constant is due to the the substitution of Cu for Cd atoms in the CdS lattice. The lattice constant decrease can be understood in terms of the difference in atomic size (ionic radii: Cu^2= 0.96 A < Cd ^2= 1.02 A) . This suggests that Cu^2 ions replace the Cd^2 ions in the lattice substitutionally, which in turn results in a smaller d value than that of undoped CdS film. There is always the possibility that some of the Cu^2 ions enter the lattice interstitially but since the d value continues to decrease as the Cu concentration increase ratio increases, it is more likely that the majority of Cu^2 ions are replacing Cd^2 ions substitutionally.

REF:

Preparation of Nanocrystalline Copper Doped CdS Thin

Films by Spray Pyrolysis Method

Najiba Abdullah Al-Hamdani Ameer Abdul Hussain Salih

Vol: 8 No: 3, July 2012 285 ISSN: 2222-8373

Preparation of Nanocrystalline Copper Doped CdS Thin

Films by Spray Pyrolysis Method

Najiba Abdullah Al-Hamdani Ameer Abdul Hussain Salih

Physics Department, Education College – Al-Mustansiriya University .

Doped cubic phase CdS thin film( p-type) was prepared by the doping of Au^+1. The undoped CdS films have a lattice constant of 5.820 A. The lattice constant increases with the increase of Au content. The increase of the lattice constant is due to the the substitution of Au for Cd atoms in the CdS lattice. The lattice increase can be understood in terms of the difference in atomic size (ionic radii: Au^+= 1.37 A ˃ Cd ^2+, 0.97 A) .The formation of Cd vacancies (VCd) is the main defect responsible for doping compensation in CdS:Au. In order to compensate the absence of one positive charge in the Au^+ when it substitutes the Cd^2, a vacancy of S^2- is needed for every-two Au+ cations present in the lattice.

REF:

Superficies y Vacío 25(4) 214-217, diciembre de 2012.

Au doping of CdS polycrystalline films prepared by co-sputtering of CdS–Cd-Au targets

Becerril M. 1

, Silva-López H. and Zelaya-Angel O.

Departamento de Física, CINVESTAV-IPN

Apdo. Postal 14-740, 07000 México, D.F.

Vargas-García J.R.

Departamento de Ingeniería en Metalurgia y Materiales, ESIQIE-IPN

(Recibido: 23 de mayo de 2012; Aceptado: 05 de septiembre de 2012).