Zintl-phase thermoelectric conversion material

A thermoelectric conversion material represented by the following chemical formula (I):

• Mg3+m-aAaB2-c-eCcEe (I)
• where
• the element A represents at least one selected from the group consisting of Ca, Sr, Ba, Nb, Zn, and Al;
• the element B represents at least one selected from the group consisting of Sb and Bi;
• the element C represents at least one selected from the group consisting of Mn, Si, and Cr;
• the element E represents at least one selected from the group consisting of Se and Te;
• the value of m is not less than −0.1 and not more than 0.4;
• the value of a is not less than 0 and not more than 0.1;
• the value of c is not less than 0 and not more than 0.1;
• the value of e is not less than 0.001 and not more than 0.06;
• the thermoelectric conversion material has a La2O3 crystal structure;
• and
• the thermoelectric conversion material has an average grain size of not less than 3 micrometers and not more than 70 micrometers.