Possibility of interstitial Na as electron donor in Yb14MgSb11

Abstract

Here, we investigate Na-doping Yb14MgSb11 as a potential route to increase carrier concentration based on an improved multiband model. Experimental transport data were collected on Yb14-xNaxMgSb11 samples prepared by ball milling and hot pressing. We show that Na increases the Seebeck coefficient and resistivity, suggesting that it behaves not as a substituent but as an interstitial electron donor under this synthesis and processing conditions, decreasing hole carrier concentration. Density functional theory (DFT) calculations of equilibrium phases, defect formation enthalpies, and band diagrams shed light on the defect-modified carrier concentrations. Depending on the equilibrium phase, Na can behave as a substitutional or interstitial defect.