Inorganic semiconductor ferroelectrics such as BiFeO3 have shown great potential in photovoltaic and other applications. Currently, semiconducting properties and the corresponding application in optoelectronic devices of hybrid organo-plumbate or stannate are a hot topic of academic research; more and more of such hybrids have been synthesized. Structurally, these hybrids are suitable for exploration of ferroelectricity. Therefore, the design of molecular ferroelectric semiconductors based on these hybrids provides a possibility to obtain new or high-performance semiconductor ferroelectrics. Here we investigated Pb-layered perovskites, and found the layer perovskite (benzylammonium)2PbCl4 is ferroelectric with semiconducting behaviours. It has a larger ferroelectric spontaneous polarization Ps=13 μC cm−2 and a higher Curie temperature Tc=438 K with a band gap of 3.65 eV. This finding throws light on the new properties of the hybrid organo-plumbate or stannate compounds and provides a new way to develop new semiconductor ferroelectrics.

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Molecular motion is one of the structural foundations for the development of functional molecular materials such as artificial motors and molecular ferroelectrics. Herein, we show that pendulum-like motion of the terminal group of a molecule causes a ferroelectric phase transition. Complex 4-methoxyanilinium tetrafluoroborate-18-crown-6 ([C(7)H(10)NO(18-crown-6)](+)[BF(4)](-), 1) shows a second-order ferroelectric phase transition at 127 K, together with an abrupt dielectric anomaly, Debye-type relaxation behavior, and the symmetry breaking confirmed by temperature dependence of second harmonic generation effect. The origin of the polarization is due to the order-disorder transition of the pendulum-like motions of the terminal para-methyl group of the 4-methoxyanilinium guest cation; that is, the freezing of pendulum motion at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. The supramolecular bola-like ferroelectric is distinct from the precedent ferroelectrics and will open a new avenue for the design of polar functional materials.

Recently, very intensive research interests have focused on the exploration of metal-organic frameworks (MOF) as potential ferroelectrics and multiferroics, which exhibit the coexistence of magnetic and ferroelectric ordering. [1][2][3][4][5][6] One example is the class of MOFs with the formula [{cationic guest molecule}{(metal ion)(formate) 3 }], [1][2][3][4] which closely resemble pure inorganic ferroelectric BaTiO 3 and multiferroic BiFeO 3 with perovskite ABO 3 -type structures in which A is the cationic guest molecule, the B is the metal ion, and the anion O is replaced by formate.It is known that most ABO 3 -type perovskite compounds display sequential structural phase transitions. [7] For example, BaTiO 3 exhibits three structural phase transitions: a paraelectric-ferroelectric transition at 393 K (cubic m3m to tetragonal 4mm phase), a ferroelectric-ferroelectric transition at 278 K (tetragonal 4mm to orthorhombic mm2 phase), and a ferroelectric-ferroelectric transition at 180 K (orthorhombic mm2 to rhombohedral 3m phase). A similar sequence is also found in KNbO 3 , that is, a polar tetragonal phase between 498 and 708 K, an orthorhombic phase between 263 and 498 K, and a rhombohedral phase below 263 K. For comparison, the recently reported MOFs based on metal formate as anionic frameworks all display only one structural phase transition with low-temperature magnetic ordering. Pioneering work on magnetic properties, dielectric behaviors, and ferroelectric explorations of metal formates has been done by the groups of Wang and Gao, [4] Kobayashi, [1] and Cheetham.[2] To our knowledge, no structural phase transition above room temperature has been reported for these metal formates, although Kobayashi and co-workers have investigated the effect of deuteration of the neutral guest molecules in MOF [Mn 3 (formate) 6 ], which did not result in a structural phase transition above room temperature. [1] Guest molecules undergoing order-disorder motions are responsible for the inducement of (or are the driving force for) structural phase transitions, which are probably distinct from hydrogen-related order-disorder motions. Usually, replacement of a hydrogen atom by a deuterium atom results in two significant changes in physical properties: 1) sharp enhancement of phase-transition temperature (T C ), such as in the ferroelectric compounds KH 2 PO 4 and KD 2 PO 4 with DT C % 90 K and antiferroelectric compounds NH 4 H 2 PO 4 and ND 4 D 2 PO 4 with DT C % 94 K; 2) enhancement of the dielectric constant by one to two orders of magnitude or striking enhancement of the saturated polarization (P s ). Consequently, molecules or cations confined in cage-like frameworks probably only display order-disorder features like the typical ferroelectric NaNO 2 , even if the disordered atoms are bonded to H atoms. To testify this assertion, it is very important and interesting to explore perdeutero MOFs to see how deuteration affects T C and the dielectric constant, that is, the isotopic effect. Encouraged by pioneering work on...

Hydrothermal reaction of (l)-N-(4'-cyanobenzy)-(S)-proline with CdCl2 as a Lewis acid catalyst and NaN3 gives colorless block compound 1, in which 1 displays a complicated 3D framework. Ferroelectric and dielectric property measurements reveal that 1 exhibits physical properties comparable to that of a typical ferroelectric compound with a dipole relaxation process and a dielectric constant of ca. 38.6 that makes it, by definition, a high dielectric material.