Method for manufacturing magnesium-based thermoelectric conversion material, method for manufacturing magnesium-based thermoelectric conversion element, magnesium-based thermoelectric conversion material, magnesium-based thermoelectric conversion element, and thermoelectric conversion device

A magnesium-based thermoelectric conversion material, comprising:

• a sintered substance of a magnesium-based compound,
• wherein grains of a reaction product are present in the sintered substance,
• each of the grains of the reaction product is constituted with a modified product and a high-concentration silicon region formed on the periphery of the modified product,
• the modified product contains magnesium at a concentration within a range equal to or higher than 30 at % and equal to or lower than 50 at %, silicon at a concentration within a range equal to or higher than 0 at % and equal to or lower than 20 at %, and oxygen at a concentration within a range equal to or higher than 40 at % and equal to or lower than 55 at %, and
• a number density of the grains of the reaction product is equal to or higher than 50 grains/mm2 and equal to or lower than 700 grains/mm2.