File Name : fig. s1.png Caption : fig. s1. thermogravimetric curves for crystals (1), (2), and (3) in the heating (1, 2, 3)-cooling (1’, 2’, 3’) circles. File Name : fig. s2.bmp Caption : fig. s2. the difference of electron density map around the m4-site in the structure of crystals (1), (2), and (3). the positive electron density is indicated by solid lines and the negative electron density is designated by dashed lines. contour intervals are 0.1 eå−3. File Name : fig. s3.jpg Caption : fig. s3. occupancy of the m(1–4) site by ca2+ and pb2+ in the crystal structures of (1), (2) and (3) crystals. File Name : fig. s4.tif Caption : fig. s4. complex impedance plot of ca5.6pb4.9(vo4)7 at selected temperatures, demonstrating absence of noticeable electronic contribution. the total electric conductivity values for the sample at 680, 720 and 810 k corresponds to (0. 23; 0.6; 2.4) 10-3 ω–1cm–1, respectively.