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A Polar Tetragonal Tungsten Bronze with Colossal Second-Harmonic Generation.

ABSTRACT: A polar tetragonal tungsten bronze, Pb_1.91 K_3.22 □_0.85 Li_2.96 Nb₁₀ O₃₀ (□: vacancies), has been successfully synthesized by a high temperature solid-state reaction. Single crystal and powder X-ray diffraction indicate that the structure of Pb_1.91 K_3.22 □_0.85 Li_2.96 Nb₁₀ O₃₀ crystallizing in the noncentrosymmetric (NCS) space group, P4bm, consists of 3D framework with highly distorted NbO₆ , LiO₉ , PbO₁₂ , and (Pb/K)O₁₅ polyhedra. While NCS Pb_1.91 K_3.22 □_0.85 Li_2.96 Nb₁₀ O₃₀ undergoes a reversible phase transition between polar (P4bm) and nonpolar (P4/mbm) structure at around 460 °C, the material decomposes to centrosymmetric Pb_1.45 K_3.56 Li_3.54 Nb₁₀ O₃₀ (P4/mbm) once heated to 1200 °C. Powder second-harmonic generation (SHG) measurements with 1064 nm radiation indicate that Pb_1.91 K_3.22 □_0.85 Li_2.96 Nb₁₀ O₃₀ exhibits a giant phase-matchable SHG intensity of ≈71.5 times that of KH₂ PO₄ , which is the strongest intensity in the visible range among all nonlinear optical materials reported to date. The observed colossal SHG should be attributable to the synergistic effect of dipole moments from the well-aligned NbO₆ octahedra, the constituting distortive channels with vacancies, and highly polarizable cations.

SUBMITTER: Kuk Y

PROVIDER: S-EPMC10323606 | biostudies-literature | 2023 Jul

REPOSITORIES: biostudies-literature

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A Polar Tetragonal Tungsten Bronze with Colossal Second-Harmonic Generation.

Kuk Yunseung Y Bae Seong Bin SB Yang Sang Mo SM Ok Kang Min KM

Advanced science (Weinheim, Baden-Wurttemberg, Germany) 20230423 19

A polar tetragonal tungsten bronze, Pb1.91 K3.22 □0.85 Li2.96 Nb10 O30 (□: vacancies), has been successfully synthesized by a high temperature solid-state reaction. Single crystal and powder X-ray diffraction indicate that the structure of Pb1.91 K3.22 □0.85 Li2.96 Nb10 O30 crystallizing in the noncentrosymmetric (NCS) space group, P4bm, consists of 3D framework wit ...[more]

PMID: 37088734

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Project description:Two-dimensional lead halide perovskites represent a fascinating class of hybrid semiconductors for solar cell, light-emitting, nonlinear optical (NLO), and ferroelectric applications. A notable subset within this category is luminescent ferroelectrics, which have garnered considerable attention for their potential in integrated photoelectronic devices. In this study, we employed an organic amine halogenation strategy (also referred to as halogen engineering), which is renowned for its efficacy in inducing polar order through crystal engineering. Consequently, we synthesized a layered Ruddlesden-Popper (RP) lead chloride comprising 3-chloropropylammonium cations (CPA+), with the chemical formula CPA2PbCl4. This compound features as many as four temperature-dependent crystal phases, with phase transitions observed at T1 = 353.1 K (343.9 K), T2 = 211.7 K (208.6 K), and T3 = 182.0 K (178.2 K) in the heating (cooling) cycles. Employing a multitechnique approach─including thermal analysis, X-ray diffraction, dielectric and pyroelectric current measurements, Raman spectroscopy, and second-harmonic generation (SHG) studies─we determined the mechanisms of the structural phase transitions. Our findings demonstrate polar order of phase II (space group Cmc21), phase III (space group Pna21), and phase IV (space group Pca21), while also confirming the centrosymmetric nature of phase I (space group Cmce). X-ray diffraction data revealed that the I to II PT is of a ferroelectric nature, devoid of ferroelastic strain, a conclusion further supported by pyroelectric measurements. CPA2PbCl4 features negative linear thermal expansion and broadband emission, which transitions to white light above 180 K. Remarkably, CPA2PbCl4 also demonstrates high-temperature SHG on-off switching with a high contrast ratio of 300:1 along with good switching stability, as evidenced by SHG cycling studies at heating/cooling rates ranging from 5 to 50 K/min. This SHG study also sets new standards for the field of SHG switching by providing a method to quantify the thermal responsiveness of SHG-switchable materials using the treq (time requirement) parameter. Overall, our findings show that the halogenation strategy has led to the discovery of a rare example of an RP perovskite exhibiting coexistence of white-light emission, SHG on-off thermal bistability, ferroelectricity, and negative linear thermal expansion.

Dataset Information

A Polar Tetragonal Tungsten Bronze with Colossal Second-Harmonic Generation.

Publications

A Polar Tetragonal Tungsten Bronze with Colossal Second-Harmonic Generation.

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