Experimental results The lattice parameters of the LaNiO$_{3}$ (LNO) films are determined from x-ray diffraction carried out at room temperature. Scans along the (0 0 L ), shown in Fig. 5a-d, are used to determine the c -axis parameters of LNO on LaAlO$_{3}$ (LAO) and SrTiO$_{3}$ (STO). The in-plane parameters are determined from HK reciprocal space maps taken about the (2 2 2)film peaks (Fig. 5e,f). In both LNO on STO and LAO, the films are found to be coherently strained to the substrates, exhibiting the same a , b parameters as the substrates. Half-order peaks, arising from the octahedral rotations, are measured to determine the oxygen positions. Figure 6 shows scans through various half-order peaks along the H and L directions, confirming that the peak widths are independent on their location on the reciprocal lattices. There are four possible domains that give rise to different structure factors for each peak. The domain volume fractions are obtained by comparing the intensities of a set of symmetrically equivalent peaks with fixed L . For LNO on STO, the equal intensities of the (1/2 3/2 1/2) family of peaks, shown in Fig. 7a, indicate the four domains have equal volume fractions. Similar scans for the LNO/LAO film (Fig. 7b) indicate unequal domain populations, with only two domains present in a ratio of 2:1. The ratio of twin domains in the LAO substrate is also 2:1 (Fig. 8) suggesting that the rotational domains present in the LNO film are imprinted from the LAO substrate. With the domain volume fractions determined, scans were carried out through multiple half-order Bragg peaks to determine the oxygen positions. The bond angles and lengths are obtained and are summarized in Table S1. 16 Supplemental Materials