The solid-solution Zintl compounds with the mixed cations of Ca²⁺and Yb²⁺ in the Ca_5-xYb_xAl₂Sb₆ (1.0 ≤ x ≤ 5.0) system have been known to be synthesized by the arc-melting method, and two slightly different crystal structures of the Ba₅Al₂Bi₆-type and Ca₅Ga₂Sb₆-type phases have been characterized using powder and single-crystal X-ray diffractions. The two phases adopt the orthorhombic space group Pbam (Z = 2, oP26) with seven independent asymmetric atomic sites in a unit cell. In our earlier investigations, we revealed that the Ca₅Ga₂Sb₆-type phase showed a better thermoelectric performance than that of the Ba₅Al₂Bi₆-type phase. With this Zintl compound, two strategies to improve ZT value have been attempted. One is the Sb/Ge anion mixing to introduce a hall doping for the Ca₅Ga₂Sb₆-type phase, and the other one is an introducing of a phase segregation from a parent Ca₅Ga₂Sb₆-type phases into a mixture containing a Ba₅Al₂Bi₆-type as well. For the Sb/Ge anion-mixing study, several compounds in the Ca₄YbAl₂Sb_6-yGe_y system containing different ratios of Sb and Ge were synthesized by arc melting. After then, the compounds underwent the phase transition from the Ba₅Al₂Bi₆-type to the Ca₅Ga₂Sb₆-type structure via annealing process at 700°C for 2 weeks. The resultant compound indeed shows an enhanced ZT value implying the hole doping was partial successful. For a phase-segregation study, as synthesized Ca_1.5Yb_3.5Al₂Sb₆ underwent an annealing process for various durations from one to three days. Once the two title phases were observed in powder X-ray diffraction experiment, a series of thermoelectric property measurements were conducted.