The La-2125 type La_2−xDy_xCa_2xBa₂Cu_4+2xO_z (0.1 ≤
x ≤
0.5; LDBO) compounds have been synthesized and studied as regards their structural and superconducting properties using room temperature neutron diffraction, high field dc magnetization, four-probe resistivity and iodometric double titration. The Rietveld analysis of the neutron diffraction data reveals tetragonal structure for all the samples, which crystallizes into La-123 type tetragonal structure in the P4/mmm space group. Iodometric double titrations were performed to determine the oxygen content values and calculate the mobile charge carrier (hole) density. The superconducting transition temperature (T_c) increases from ~20 K for x = 0.1 to a maximum of 75 K for x = 0.5. The flux pinning force (F_p) and critical current density (J_c), calculated from the low temperature hysteresis loops, also increasewith increasing dopant concentration. This paper presents studies on the structure and superconducting properties of all LDBO compounds in relation to the role of calcium in inducing superconductivity in the tetragonal non-superconducting oxide.