Thermoelectric material, manufacturing method of thermoelectric material, thermoelectric conversion element, and thermoelectric conversion module

A thermoelectric material comprising a sintered body formed of p-type and n-type thermoelectric materials for a thermoelectric conversion element, the thermoelectric materials represented by a composition formula shown below, and having a MgAgAs type crystal structure as a main phase,

• (Tia1Zrb1Hfc1)xαyβ100-x-y
• where 0<a1≤1, 0<b1≤1, 0<c1≤1, a1+b1+c1=1, 30≤x≤35, and 30≤y≤35;
• in the n-type thermoelectric materials, α is Ni, β is Sn, and 30 atomic % or less of β is substituted by at least one element selected from the group consisting of Si, Mg, As, Sb, Bi, Ge, Pb, Ga and In;
• and in the p-type thermoelectric materials, α is Co, β is Sb, and 30 atomic % or less of β is substituted by at least one element selected from the group consisting of Sn, Si, Mg, As, Bi, Ge, Pb, Ga, and In,
• wherein an area ratio of internal defects of the thermoelectric materials for one thermoelectric conversion element is 10% or less in terms of a total area ratio of defective portions in a scanning surface according to ultrasonic flaw detection in a thickness direction with respect to a surface parallel with one plane of the thermoelectric material under conditions:
• frequency, 200 MHz;
• focal length, 2.9 mm;
• scanning pitch, 2.5 μm;
• scanning surface size, 2 mm×3 mm;
• a Cu plate (0.25 mm thick) is bonded on both sides of a sample (1 mm thick);
• and lower limit defect length, 3 μm;
• and no defect having a length of 800 μm or more is present at any vertex of chips of the thermoelectric materials.