During the last decades, solid-state materials with cooperative electric order, namely, ferro‑, ferri- or antiferroelectric properties, have attracted great attention within scientist working in very diverse areas, from theoretical physics and chemistry to materials technology. These materials display significant applications in electric and electronic devices, such as capacitors, data storage memories, pressure and temperature sensors, photoferroelectric, and so on.[1] In this context, recently, the methylammonium lead triiodide compound, (CH₃NH₃)PbI₃, with perovskite-type structure, has set an unprecedented breakthrough in the field of photovoltaic applications.[2] In addition, this material also exhibit very interesting dielectric properties, where (CH₃NH₃)PbI₃ displays two dielectric transition at T=162 K and T=330 K related to a phase order transition.[3] Nowadays, there is an open debate and discussion about the possible ferroelectricity of this compound as well as about the origin of the large dielectric constant at room temperature and low frequency. [4]In this work, we have focused on the dimethylammonium [(CH₃)₂NH₂]PbI₃perovskite,which is an analogue compound to the intensively studied methylammonium (CH₃NH₃)PbI₃. Very interestingly, [(CH₃)₂NH₂]PbI₃ shows a dielectric anomaly associated with a phase transition at T = 260 K. We attribute it to an antiferroelectric to paraelectric phase transition due to an antiparallel arrangement of both polar [PbI₆] chains and polar DMA cations in the low temperature LT-phase, which become nonpolar and disordered, respectively, in the high temperature HT-phase. Additionally, this compound exhibits giant values of the dielectric constant at room temperature and low frequencies, as previously observed in the analogous (CH₃NH₃)PbI₃ compound,[4b] that we attribute to the appearance of a certain conductivity and the activation of extrinsic contributions, as demonstrated by impedance spectroscopy. The large optical band gap displayed by this material rules out that the observed conductivity can be electronic and points out to ionic conductivity, as confirmed by DFT calculations that have shown the paths of minimum energy (E_a=0.68 eV) for the movement of the I- anions.[5]  

[1]C. N. R. Rao, J. Gopalakrishnan, in New Directions in Solid State Chemistry, Cambridge University Press, 1997

[2] M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami and H. J. Snaith, Science, 2012, 338, 643

[3] N. Onoda-Yamamuro, T. Matsuo and H. Suga, J. Phys. Chem. Solids, 1992, 53, 935.

[4] (a) Z. Fan, J. Xiao, K. Sun, L. Chen, Y. Hu, J. Ouyang, K. P. Ong, K. Zeng and J. Wang, J. Phys. Chem. Lett., 2015, 6, 1155. (b) E. J. Juarez-Perez, R. S. Sanchez, L. Badia, G. Garcia-Belmonte, Y. S. Kang, I. Mora-Sero and Juan Bisquert, J. Phys. Chem. Lett., 2014, 5, 2390.

[5] A. García-Fernández, J. M. Bermúdez-García, S. Castro-García, A. L. Llamas-Saiz, R. Artiaga, J. López-Beceiro, S. Hu, W. Ren, A. Stroppa, M. Sánchez-Andújar and M. A. Señarís-Rodríguez, J. Mater. Chem. C (submmitted).