Structure and properties of the transition-metal zintl compounds A₁₄MnPn₁₁ (A = Ca, Sr, Ba; Pn = As, Sb)

The compounds A₁₄MnPn₁₁ (A = Ca, Sr, Ba; Pn = As, Sb), have been synthesized by reacting the elements in stoichiometric amounts in welded Nb tubes sealed in quartz ampules at high temperature (1250°C). Single-crystal X-ray data (130 K, tetragonal, I4₁/acd (142), Z = 8) were refined for all compounds except Ba₁₄MnAs₁₁: a = 16.688 (8) Å, c = 22.266 (9) Å (R = 5.82%, R_w = 6.95%, Ca₁₄MnSb₁₁); a = 17.511 (4), c = 23.321 (7) Å, (R = 4.07%, R_w = 3.93%, Sr₁₄MnSb₁₁); a = 18.394 (3), c = 24.069 (6) Å (R = 7.52%, R_w = 6.96%, Ba₁₄MnSb₁₁); a = 15.754 (3), c = 21.037 (7) Å (R = 4.09%, R2 = 8.82%, Ca₁₄Mn As₁₁); a = 16.576 (10), c = 22.167 (14) Å (R = 5.70%, R_w = 4.87%, Sr₁₄MnAs₁₁). These compounds are isostructural to the main-group Zintl compound Ca₁₄AlSb₁₁. Magnetization measurements performed on powder samples have shown that the antimony compounds are ferromagnets with ordering temperatures of 65 (Ca), 45 (Sr), and 20 K (Ba), whereas the arsenic compounds are paramagnetic down to 5 K. The temperature dependence of the resistivity of pressed pellets indicates that the Sb compounds may be metallic and the As compounds are semiconductors.