[(CH₃)₂NH₂]₇Pb₄X₁₅ (X = Cl^– and Br^–), 2D-Perovskite Related Hybrids with Dielectric Transitions and Broadband Photoluminiscent Emission

We have prepared two new lead halides with the novel general formula of DMA₇Pb₄X₁₅ (DMA = [(CH₃)₂NH₂]⁺ and X = Cl^– or Br^–) by using an easy route under mild conditions at room temperature. These compounds exhibit an unprecedented crystal structure, are formed by layers of distorted [PbX₆] octahedra, which share corners and faces, and contain intercalated DMA cations. Very interestingly, they display dielectric transitions, which are related to a partial order–disorder process of the DMA cations between 160 and 260 K. Additionally, these new layered hybrids exhibit a broadband photoluminiscent emission, which is related to the structural distortions of the [PbX₆] octahedra. These findings not only open up large possibilities for future optoelectronic applications of these materials, but they also offer a novel playground for an easy modulation of electrical and optical properties of hybrid organic–inorganic materials. We anticipate that this novel A₇Pb₄X₁₅ formula can be adequate to tune the family of the hybrid lead halides using other alkylammonium cations, such as methylammonium, formamidinium, or ethylammonium, to improve their photoelectronic properties

Role of Temperature and Pressure on the Multisensitive Multiferroic Dicyanamide Framework [TPrA][Mn(dca)₃] with Perovskite-like Structure

A multistimuli response to temperature and pressure is found in the hybrid inorganic–organic perovskite-like [TPrA]­[Mn­(dca)₃] compound, which is related to a first-order structural phase transition near room temperature, <i>T</i>_t ≈ 330 K. This phase transition involves a transformation from room temperature <i>polymorph I</i>, with the noncentrosymmetric space group <i>P</i>4̅2₁<i>c</i>, to the high temperature <i>polymorph II</i>, with the centrosymmetric space group <i>I4/mcm</i>, and it implies ionic displacements, order–disorder phenomena, and a large and anisotropic thermal expansion (specially along the <i>c</i>-axis). As a consequence, [TPrA]­[Mn­(dca)₃] exhibits a dielectric anomaly, associated with the change from a cooperative to a noncooperative electric behavior (antiferroelectric (AFE)–paraelectric (PE) transition). The former implies an AFE distribution of electric dipoles in <i>polymorph I</i>, related to the described off-shift of the apolar TPrA cations and the order–disorder of the polar dca ligands mechanisms, that are different from those reported, up to now, for others perovskite-type hybrid compounds. Such cooperative electric order, below <i>T</i>_t ≈ 330 K, coexisting with long-range antiferromagnetic ordering below <i>T</i> = 2.1 K render the [TPrA]­[Mn­(dca)₃] a new type-I multiferroic material. In addition, the obtained experimental results reveal that this compound is also a multistimuli-responsive material, with a very large sensitivity toward temperature and applied external pressure, δ<i>T</i>_t/δ<i>P</i> ≈ 24 K kbar^–1, even for small values of pressure (<i>P</i> < 2 kbar). Therefore, this material opens up a potential interest for future technological applications, such as temperature/pressure sensing

Role of Temperature and Pressure on the Multisensitive Multiferroic Dicyanamide Framework [TPrA][Mn(dca)₃] with Perovskite-like Structure

A multistimuli response to temperature and pressure is found in the hybrid inorganic–organic perovskite-like [TPrA]­[Mn­(dca)₃] compound, which is related to a first-order structural phase transition near room temperature, <i>T</i>_t ≈ 330 K. This phase transition involves a transformation from room temperature <i>polymorph I</i>, with the noncentrosymmetric space group <i>P</i>4̅2₁<i>c</i>, to the high temperature <i>polymorph II</i>, with the centrosymmetric space group <i>I4/mcm</i>, and it implies ionic displacements, order–disorder phenomena, and a large and anisotropic thermal expansion (specially along the <i>c</i>-axis). As a consequence, [TPrA]­[Mn­(dca)₃] exhibits a dielectric anomaly, associated with the change from a cooperative to a noncooperative electric behavior (antiferroelectric (AFE)–paraelectric (PE) transition). The former implies an AFE distribution of electric dipoles in <i>polymorph I</i>, related to the described off-shift of the apolar TPrA cations and the order–disorder of the polar dca ligands mechanisms, that are different from those reported, up to now, for others perovskite-type hybrid compounds. Such cooperative electric order, below <i>T</i>_t ≈ 330 K, coexisting with long-range antiferromagnetic ordering below <i>T</i> = 2.1 K render the [TPrA]­[Mn­(dca)₃] a new type-I multiferroic material. In addition, the obtained experimental results reveal that this compound is also a multistimuli-responsive material, with a very large sensitivity toward temperature and applied external pressure, δ<i>T</i>_t/δ<i>P</i> ≈ 24 K kbar^–1, even for small values of pressure (<i>P</i> < 2 kbar). Therefore, this material opens up a potential interest for future technological applications, such as temperature/pressure sensing