In2Ge2O7 and In2Si2O7 are commonly used as scintillation materials. More studies on In2X2O7 (X=C, Si, Ge, or Sn) are important to explore the possibility of using these materials for optoelectronic devices. This work presents results dealing with structural properties, electronic structure, chemical bonding, carrier effective masses, and optical spectra of polymorphs of In2X2O7 obtained from first-principles calculations. The monoclinic phase of In2Ge2O7, cubic and monoclinic phases of In2Si2O7, as well as cubic phase of In2Sn2O7 are known in scientific literature. From the total energy calculations at high pressure/strain we have found that the monoclinic phase of In2Si2O7, In2Ge2O7, and In2Sn2O7 can be transformed into the cubic phase. The cubic phase of In2Ge2O7 and In2Sn2O7 is found to be more stable than the monoclinic phase. However, the monoclinic phase of In2C2O7 and In2Si2O7 is more stable than the cubic phase. The phase stability study suggests that In2C2O7 is not stable, and that it might dissociate into corresponding binary oxides. Effective masses of electrons and holes have been estimated. Analysis of optical properties shows that in Si solar cells In2Si2O7 and In2Sn2O7 can be used as antireflection coating layer. (C) 2011 Elsevier B.V. All rights reserved.