Cation Ordering and Electrical Properties of the Ruddlesden‐Popper Gd 2−2x Sr 1+2x Co 2 O 7 Compounds (x = 0 and 0.10)

We report the structure and microstructure of the Ruddlesden‐Popper (RP) series n=2 Gd 2−2x Sr 1+2x Co 2 O 7 (x = 0 and 0.10). X‐ray powder diffraction, electron diffraction and HRTEM indicate that these compounds have a tetragonal structure (space group: P 4 2 / mnm ) with cell parameters a ≈ 5.3749Å c ≈ 19.3591Å, in which the [CoO 6 ] octahedra are distorted and tilted. Also, very interestingly, according to the obtained results these compounds presents A‐site cation ordering where the divalent and bigger Sr 2+ cation selectively prefers the 12‐coordinated P site while the smaller and trivalent Gd 3+ cation prefers the 9‐coordinated R site. From the electrical point of view these materials are semiconducting and their resistivitiy decreases upon doping. In addition, the highest doped sample presents a small magnetoresistive effect MR max = −3.2 % under H max = 50 kOe at T = 55 K.