文摘
Ba1.9Ca2.4Mg9.7Si7 was grown as large crystals from the reaction of silicon with barium and calcium in Mg/Al flux. This compound is a charge-balanced Zintl phase with the Zr2Fe12P7 structure type in hexagonal space group P6虆 (a = 11.196(2) 脜, c = 4.4595(9) 脜); barium occupies the Zr sites, the lighter alkaline earths (Mg, Ca) mix on the Fe sites, and silicon occupies the phosphorus sites. An isostructural germanide (Ba1.2Sr0.9Mg11.9Ge7, a = 11.064(1) 脜, c = 4.3709(6) 脜)) was similarly synthesized from reactions of germanium with barium and strontium in Mg/Al flux. Density of states calculations indicate these phases are semimetals, in agreement with their charge-balanced nature. Measurements of electrical resistivity, thermal conductivity, and Seebeck coefficient were carried out from 300鈥?000 K to investigate the thermoelectric properties of Ba1.9Ca2.4Mg9.7Si7. This compound is an n-type semimetal with low thermal conductivity (2 W/(m路K)), moderate Seebeck coefficient (鈭?00 渭V/K at 900 K), and a thermoelectric figure of merit ZT of 0.35 at 900 K.