Tianliang Chen

Bis(imidazolium) L‐Tartrate: A Hydrogen‐Bonded Displacive‐Type Molecular Ferroelectric Material

A hydrogen-bonded ionic cocrystal with imidazole as molecular rotator and L-tartaric acid as homochiral component is reported as a displacive-type ferroelectric material. It undergoes a paraelectric-ferroelectric phase transition at 252 K with exceptional dielectric responses triggered by atomic displacements.

Deep-ultraviolet transparent phosphates RbBa2(PO3)5 and Rb2Ba3(P2O7)2 show nonlinear optical activity from condensation of [PO4](3-) units.

It is challenging to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance between deep-UV transparency and high NLO activity. Known deep-UV NLO materials are almost exclusively limited to borates, except few newly discovered phosphates despite their small NLO activities. Here we report two asymmetric phosphates, RbBa2(PO3)5 (I) and Rb2Ba3(P2O7)2 (II), which feature [PO3]∞ chains and [P2O7](4-) dimers formed by condensation of [PO4](3-) units, respectively. Remarkably, I achieves the desired balance, with the shortest deep-UV absorption edge at 163 nm and the largest NLO activity of 1.4 × KDP (KH2PO4) in deep-UV NLO phosphates. According to first-principles calculations, the enhanced macroscopic SHG response of I can be attributed to the [PO3]∞ chains which exhibit significantly larger microscopic SHG coefficients as compared with the [P2O7](4-) dimers.

N-Isopropylbenzylammonium tetrafluoroborate: an organic dielectric relaxor with a tunable transition between high and low dielectric states

An organic dielectric relaxor, N-isopropylbenzylammonium tetrafluoroborate (1), with tunable dielectric properties between high and low dielectric states, has been successfully constructed through the prominent strategies of reversible structure transitions associated with ordering and reorientation of molecular motions. 1 undergoes an exceptional order–disorder solid state phase transition at 201 K, which was confirmed by the variable temperature single crystal X-ray diffraction analysis, thermal analysis and dielectric measurements. Owing to the ordering of the pendulum-like motion of methyl groups in the N-isopropylbenzylammonium (N-IPBA) cations and the reorientation of the molecular dipoles, 1 demonstrates a phase transition from a space group of C2/m at room temperature to C2/c at low temperature. Emphatically, the striking anisotropy of the dielectric response was investigated, revealing the crucial role of the ordering and orientation motions of N-IPBA cations. Moreover, the significant dielectric relaxation behaviour, attributed to the orientational polarization of the molecules’ dipoles, was observed and discussed. Such distinctive dielectric performances suggest that 1 might be a potential switchable relaxor-type dielectric material.

Ultrahigh Pyroelectric Figures of Merit Associated with Distinct Bistable Dielectric Phase Transition in a New Molecular Compound: Di‐n‐Butylaminium Trifluoroacetate

Ultrahigh pyroelectric figures of merit are achieved in a new phase-transition material, di-n-butylaminium trifluoroacetate, of which the peak values are an order of magnitude larger than those of their inorganic counterparts. Such an attractive behavior of pyroelectric detectivity is strongly related to its distinct bistable dielectric behavior, which recalls excellent thermoelectric response in organic molecular phase-transition systems.

Switchable dielectric behaviour associated with above room-temperature phase transition in N-isopropylbenzylammonium dichloroacetate (N-IPBADC)

A bulk transparent single-crystal of N-isopropylbenzylammonium dichloroacetate (N-IPBADC) with sizes of 15 × 15 × 10 mm3, which possesses switchable dielectric permittivities above room temperature, has been successfully grown by the slow solution cooling method. A reversible second-order solid-state phase transition at 366 K was confirmed by thermal analyses, including differential scanning calorimetry (DSC) and specific heat (Cp), dielectric measurements, variable-temperature single-crystal X-ray diffraction and powder X-ray diffraction (PXRD). In particular, order–disorder transformations of the dichloroacetate moieties in N-IPBADC from room temperature to high temperature phases have been revealed to induce the distinct dielectric anomaly along with dielectric anisotropic properties above room temperature, up to 366 K. The successful discovery of N-IPBADC would potentially pave a new way to explore new above room-temperature phase transition materials.

An organic–inorganic hybrid co-crystal complex as a high-performance solid-state nonlinear optical switch

Solid-state nonlinear optical (NLO) switches have attracted great interest, while high performance solid-state nonlinear optical (NLO) switches still remain scarce. Herein, we firstly present a high-performance solid-state NLO switch based on an organic–inorganic hybrid co-crystal complex, [H2dabcoCl2][FeCl3(H2O)3] (1, dabco = 1,4-diazabicyclo[2.2.2]octane). It is found that 1 exhibits a moderately large NLO response of ∼0.31 pm V−1, a superior switching contrast (∼25) and a highly tunable repeatability, which may guarantee its potential device applications. In addition, microscopic crystal structural analyses reveal that its NLO switching is attributed to the order–disorder transformation of the dabco cation, cooperating with the reorientational displacement of the inorganic [FeCl3(H2O)3] component. Owing to the broader designability of organic–inorganic hybrids, this work opens up an attractive approach for exploring new high-performance NLO switches.

Bulk crystal growth and characterization of imidazolium L-tartrate (IMLT): a novel organic nonlinear optical material with a high laser-induced damage threshold

Bulk transparent organic nonlinear optical (NLO) single-crystals of imidazolium L-tartrate (IMLT), with a low near-UV cutoff wavelength at 235 nm and a large powder second harmonic generation (SHG) efficiency, being 4.5 times larger than that of KH2PO4 (KDP), have been successfully grown by the slow cooling method. Kurtz and Perry powder test reveals that IMLT is a phase-matchable NLO material with good optical transmittance in the entire visible region. The laser-induced damage threshold experiments show that the grown IMLT bulk crystals possess an excellent resistance to laser radiation with a high threshold up to 7.45 GW cm−2, much larger than those of several known inorganic and organic NLO materials. Furthermore, the thermal properties associated with its high laser-induced damage threshold, including the specific heat and thermal expansion coefficients, have been investigated thoroughly as a function of temperature. The intrinsic origin of the laser-induced damage was also analyzed based on studying the surface morphologies triggered with the laser-induced damage using an optical microscope. All the findings in the present work indicate that IMLT has a potential application as a useful NLO candidate.

Phase Transition Originating from Order–Disorder Transformations of Carboxy Oxygen Atoms Coupled with Dynamic Proton Motions in [PhCH2NH(CH3)2]2C2O4⋅H2C2O4

A new molecular phase transition material, [PhCH(2) NH(CH(3))(2)](2) C(2)O(4)⋅H(2)C(2)O(4), which undergoes a reversible phase transition at 151.6 K, has been successfully synthesized. Differential scanning calorimetry (DSC), specific heat capacity, and dielectric measurements confirm its reversible phase transition with a large thermal hysteresis of 15.1 K, demonstrating that the phase transition is typical first order. Variable-temperature single-crystal X-ray diffraction analyses reveal that the order-disorder transformations of carboxy oxygen atoms induce the structural phase transition. A slight reorientation of the oxalic acid unit is discovered to accompany the ordering of carboxy oxygen atoms at low temperature. The DSC measurement result of the deuterated analog is different to that of 1, indicating that proton dynamic motions in hydrogen bonds also contribute to the phase transition.

Synthesis, growth and characterization of a third-order nonlinear optical crystal based on the borate ester with sodium supporting its structural framework

A novel third-order nonlinear optical (NLO) crystal based on the organic borate carboxylate ester, with formula [Na4(H2O)5][B{O2CCH(O)Ph}2]4 (abbreviated as LMBNa), has been prepared in aqueous solution. Single-crystal X-ray diffraction analysis reveals that the boron atom is coordinated with two L-mandelic ligands by alkoxide and carboxylate groups, forming the [B{OOCCH(O)C6H5}]− anion. The sodium cation supports its structural framework of borate anions in the formation of a cross-linked structure. Bulk single crystals of LMBNa were grown from acetonitrile/water by the temperature lowering method. Studies of its third-order NLO properties using a Z-scan technique demonstrate that the LMBNa crystal possesses a strong saturable absorption and the self-focusing effect. Its second molecular hyperpolarizability (γ) at 532 nm is calculated to be (3.9 ± 0.2) × 10−31 esu. Furthermore, dielectric experiments reveal that LMBNa has a quite low-dielectric constant (∼3.43) and shows an anisotropy of frequency dependence along the different crystallographic directions. Such dielectric behaviors will favor the application of the LMBNa crystal under the electric field. All the results indicate that LMBNa might be a potential candidate material for the third-order NLO applications.

Switchable Dielectric Phase Transition Induced by a Twisting Transformation in Diglycine Methanesulfonate

A new glycine-based reversible phase transition compound diglycine methanesulfonate (1) has been successfully synthesized. Differential scanning calorimetry (DSC) measurements of 1 showed a pair of broad peaks around 134 K (T(c)=phase transition temperature) with a slight thermal hysteresis during the heating/cooling cycle, thereby indicating that this compound undergoes a reversible second-order phase transition. Dielectric measurements further confirmed the phase transition and revealed a switchable response to the ambient temperature change for the dielectric constants of 1, namely, the dielectric constants have a distinctive step-like anomaly switching between a high dielectric state in the room temperature phase (RTP) and a low state in the low temperature phase (LTP). Variable-temperature single-crystal X-ray diffraction analyses show that 1 undergoes an atypical transition from the space group P2₁/m in the RTP to P2₁/c in the LTP. The origin of the switchable dielectric phase transition is ascribed to the movement of the moieties in 1 from the equilibrium position, and this stems from the twisting of the molecules in the compound. We believe that these findings will be useful in exploring switchable dielectric phase transition materials.