Electronic and transport properties of polycrystalline Ba8Ga15Ge31 type I clathrate prepared by SPS method

► Scanning thermoelectric microprobe STMP measurements show important uniformity change during sample annealing. ► Calculated band gap Eg values are close to the reported Eg. ► Ga/Ge ratio change doesn't affect significantly the bonding properties. ► Band structure calculations show that bond's character agrees with the Zintl concept.