The C3D10T elements is identical to the C3D10 element except for the treatment of thermal strains. In a regular C3D10 element both the initial temperatures and the displacements are interpolated quadratically, which leads to quadratic thermal strains and linear total strains (since the total strain is the derivative of the displacements). The mechanical strain is the total strain minus the thermal strain, which is consequently neither purely linear nor purely quadratic. This discrepancy may lead to a checkerboard pattern in the stresses, which is observed especially in the presence of high initial temperature gradients. To alleviate this the initial temperatures are interpolated linearly within the C3D10T element.
Notice that the linear interpolation of the initial temperatures is standard for the C3D20 and C3D20R element. For the C3D10 element it is not to keep the compatibily with ABAQUS.