Bibliografía

Reaction of the anion-deficient, cation-ordered perovskite phase Ba₂YFeO₅ with 80 atm of oxygen pressure at 410 °C results in the formation of the Fe⁴⁺ phase Ba₂YFeO_5.5. The topochemical insertion of oxide ions lifts the inversion symmetry of the centrosymmetric host phase, Ba₂YFeO₅ (space group <i>P</i>2₁/<i>n</i>), to yield a noncentrosymmetric (NCS) phase Ba₂YFeO_5.5 (space group <i>Pb</i>2₁<i>m</i> (No. 26), <i>a</i> = 12.1320(2) Å, <i>b</i> = 6.0606(1) Å, <i>c</i> = 8.0956(1) Å, <i>V</i> = 595.257(2) ų) confirmed by the observation of second-harmonic generation. Dielectric and PUND ferroelectric measurements, however, show no evidence for a switchable ferroelectric polarization, limiting the material to pyroelectric behavior. Magnetization and low-temperature neutron diffraction data indicate that Ba₂YFeO_5.5 undergoes a magnetic transition at 20 K to adopt a state which exhibits a combination of ferromagnetic and antiferromagnetic order. The symmetry breaking from centrosymmetric to polar noncentrosymmetric, which occurs during the topochemical oxidation process is discussed on the basis of induced lattice strain and an electronic instability and represents a new strategy for the preparation of NCS materials that readily incorporate paramagnetic transition metal centers

Top-Seeded Solution Crystal Growth and Functional Properties of Polar LiFeP₂O₇

Large single crystals of LiFeP₂O₇, a multifunctional polar material, were successfully grown by using a top-seeded solution growth (tssg) technique. The morphologies of the single crystals with different rotation speeds are described. Functional properties such as second-harmonic generation (SHG), piezoelectricity, pyroelectricity, and ferroelectricity were measured. LiFeP₂O₇ is SHG active, with an SHG efficiency of approximately 200 × α-SiO₂ using 1064 nm radiation. The material is piezoelectric, with a <i>d</i>₂₂ value of 1.2 pC/N, and pyroelectric, with pyroelectric coefficients of 9.25 μC/m²K (1 kHz) and 10.6 μC/m²K (50 Hz) at 60 °C. Although polar, LiFeP₂O₇ is not ferroelectric; that is, the polarization is not “switchable”. Optical spectra indicate that the absorption edge is approximately 480 nm, with transmission up to 4.3 μm

Synthesis, Structure, and Characterization of New Li⁺ – d⁰ –Lone-Pair – Oxides: Noncentrosymmetric Polar Li₆(Mo₂O₅)₃(SeO₃)₆ and Centrosymmetric Li₂(MO₃)(TeO₃) (M = Mo⁶⁺ or W⁶⁺)

New quaternary lithium – d⁰ cation – lone-pair oxides, Li₆(Mo₂O₅)₃(SeO₃)₆ (<i>Pmn</i>2₁) and Li₂(MO₃)­(TeO₃) (<i>P</i>2₁/<i>n</i>) (M = Mo⁶⁺ or W⁶⁺), have been synthesized and characterized. The former is noncentrosymmetric and polar, whereas the latter is centrosymmetric. Their crystal structures exhibit zigzag anionic layers composed of distorted MO₆ and asymmetric AO₃ (A = Se⁴⁺ or Te⁴⁺) polyhedra. The anionic layers stack along a 2-fold screw axis and are separated by Li⁺ cations. Powder SHG measurements on Li₆(Mo₂O₅)₃(SeO₃)₆ using 1064 nm radiation reveal a SHG efficiency of approximately 170 × α-SiO₂. Particle size vs SHG efficiency measurements indicate Li₆(Mo₂O₅)₃(SeO₃)₆ is type 1 nonphase-matchable. Converse piezoelectric measurements result in a d₃₃ value of ∼28 pm/V and pyroelectric measurements reveal a pyroelectric coefficient of −0.43 μC/m²K at 50 °C for Li₆(Mo₂O₅)₃(SeO₃)₆. Frequency-dependent polarization measurements confirm that Li₆(Mo₂O₅)₃(SeO₃)₆ is nonferroelectric, i.e., the macroscopic polarization is not reversible, or ‘switchable’. Infrared, UV–vis, thermogravimetric, and differential thermal analysis measurements and electron localization function calculations were also done for all materials

New Fluoride Carbonates: Centrosymmetric KPb₂(CO₃)₂F and Noncentrosymmetric K_2.70Pb_5.15(CO₃)₅F₃

Two new potassium lead fluoride carbonates, KPb₂(CO₃)₂F and K_2.70Pb_5.15(CO₃)₅F₃, have been synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. KPb₂(CO₃)₂F and K_2.70Pb_5.15(CO₃)₅F₃ were structurally characterized by single crystal X-ray diffraction and exhibit two-dimensional crystal structures consisting of corner-shared PbO₆F and PbO₆F₂ polyhedra. K_2.70Pb_5.15(CO₃)₅F₃ is noncentrosymmetric, and crystallizes in the <i>achiral</i> and <i>nonpolar</i> space group <i>P</i>6̅<i>m</i>2 (crystal class −6m2). Powder second-harmonic generation (SHG) measurements using 1064 nm radiation revealed a SHG efficiency of approximately 40 × α-SiO₂, whereas a charge constant, <i>d</i>₃₃, of approximately 20 pm/V was obtained through converse piezoelectric measurements. For the reported materials, infrared, UV–vis, thermogravimetric, and differential thermal analysis measurements were performed

Synthesis, Structure, and Characterization of New Li⁺ – d⁰ –Lone-Pair – Oxides: Noncentrosymmetric Polar Li₆(Mo₂O₅)₃(SeO₃)₆ and Centrosymmetric Li₂(MO₃)(TeO₃) (M = Mo⁶⁺ or W⁶⁺)

New quaternary lithium – d⁰ cation – lone-pair oxides, Li₆(Mo₂O₅)₃(SeO₃)₆ (<i>Pmn</i>2₁) and Li₂(MO₃)­(TeO₃) (<i>P</i>2₁/<i>n</i>) (M = Mo⁶⁺ or W⁶⁺), have been synthesized and characterized. The former is noncentrosymmetric and polar, whereas the latter is centrosymmetric. Their crystal structures exhibit zigzag anionic layers composed of distorted MO₆ and asymmetric AO₃ (A = Se⁴⁺ or Te⁴⁺) polyhedra. The anionic layers stack along a 2-fold screw axis and are separated by Li⁺ cations. Powder SHG measurements on Li₆(Mo₂O₅)₃(SeO₃)₆ using 1064 nm radiation reveal a SHG efficiency of approximately 170 × α-SiO₂. Particle size vs SHG efficiency measurements indicate Li₆(Mo₂O₅)₃(SeO₃)₆ is type 1 nonphase-matchable. Converse piezoelectric measurements result in a d₃₃ value of ∼28 pm/V and pyroelectric measurements reveal a pyroelectric coefficient of −0.43 μC/m²K at 50 °C for Li₆(Mo₂O₅)₃(SeO₃)₆. Frequency-dependent polarization measurements confirm that Li₆(Mo₂O₅)₃(SeO₃)₆ is nonferroelectric, i.e., the macroscopic polarization is not reversible, or ‘switchable’. Infrared, UV–vis, thermogravimetric, and differential thermal analysis measurements and electron localization function calculations were also done for all materials

Synthesis, Structure, and Characterization of Two New Polar Sodium Tungsten Selenites: Na₂(WO₃)₃(SeO₃)·2H₂O and Na₆(W₆O₁₉)(SeO₃)₂

Two new quaternary sodium tungsten selenites, Na₂(WO₃)₃(SeO₃)·2H₂O (<i>P</i>3₁<i>c</i>) and Na₆(W₆O₁₉)­(SeO₃)₂ (<i>C</i>2), have been synthesized and characterized. The former exhibits a hexagonal tungsten oxide layered structure, whereas the latter has a one-dimensional “ribbon” structure. The layers and “ribbons” consist of distorted WO₆ and asymmetric SeO₃ polyhedra. The layers in Na₂(WO₃)₃(SeO₃)·2H₂O and the “ribbons” in Na₆(W₆O₁₉)­(SeO₃)₂ are separated by Na⁺ cations. Powder second-harmonic-generation (SHG) measurements on Na₂(WO₃)₃(SeO₃)·2H₂O and Na₆(W₆O₁₉)­(SeO₃)₂ using 1064 nm radiation reveal SHG efficiencies of approximately 450× and 20× α-SiO₂, respectively. Particle size versus SHG efficiency measurements indicate that the materials are type 1 non-phase-matchable. Converse piezoelectric measurements result in <i>d</i>₃₃ values of approximately 23 and 12 pm/V, whereas pyroelectric measurements reveal coefficients of −0.41 and −1.10 μC/m²·K at 60 °C for Na₂(WO₃)₃(SeO₃)·2H₂O and Na₆(W₆O₁₉)­(SeO₃)₂, respectively. Frequency-dependent polarization measurements confirm that the materials are nonferroelectric; i.e., the macroscopic polarization is not reversible, or “switchable”. IR and UV–vis spectroscopy, thermogravimetric and differential thermal analysis measurements, and electron localization function calculations were also done for the materials. Crystal data: Na₂(WO₃)₃(SeO₃)·2H₂O, trigonal, space group <i>P</i>3₁<i>c</i> (No. 159), <i>a</i> = 7.2595(6) Å, <i>b</i> = 7.2595(6) Å, <i>c</i> = 12.4867(13) Å, <i>V</i> = 569.89(9) ų, <i>Z</i> = 2; Na₆(W₆O₁₉)­(SeO₃)₂, monoclinic, space group <i>C</i>2 (No. 5), <i>a</i> = 42.169(8) Å, <i>b</i> = 7.2690(15) Å, <i>c</i> = 6.7494(13) Å, β = 98.48(3)°, <i>V</i> = 2046.2(7) ų, <i>Z</i> = 4

Large Birefringent Materials, Na₆Te₄W₆O₂₉ and Na₂TeW₂O₉: Synthesis, Structure, Crystal Growth, and Characterization

A new d⁰ transition metal tellurite, Na₆Te₄W₆O₂₉, was synthesized by solid-state methods. The material crystallizes in monoclinic space group <i>P</i>2₁/<i>c</i> (No. 14) with the following values: <i>a</i> = 7.3297(3) Å, <i>b</i> = 21.9057(9) Å, <i>c</i> = 10.2871(3) Å, β = 133.490(2)°, and <i>Z</i> = 2. Additionally, large crystals of Na₆Te₄W₆O₂₉ (13 mm × 11 mm × 10 mm) and Na₂TeW₂O₉ (23 mm × 5 mm × 3 mm) were grown by the top seeded solution growth method. In addition to the crystal growth, refractive indices were measured, and the Sellmeier equations were fitted by using the minimum deviation technique. Interestingly, the two reported compounds exhibit relatively large birefringences: Δ<i>n</i>₃ = <i>n</i>_<i>z</i> – <i>n</i>_<i>x</i> = 0.0828–0.1248 from 1062.6 to 450.2 nm for Na₆Te₄W₆O₂₉, and Δ<i>n</i>₃ = <i>n</i>_<i>z</i> <i>– n</i>_<i>x</i> = 0.1471–0.2069 from 1062.6 to 450.2 nm for Na₂TeW₂O₉. The results indicate that Na₆Te₄W₆O₂₉ and Na₂TeW₂O₉ may have uses in applications involving birefrigent materials

Role of Acentric Displacements on the Crystal Structure and Second-Harmonic Generating Properties of RbPbCO₃F and CsPbCO₃F

Two lead fluorocarbonates, RbPbCO₃F and CsPbCO₃F, were synthesized and characterized. The materials were synthesized through solvothermal and conventional solid-state techniques. RbPbCO₃F and CsPbCO₃F were structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of corner-shared PbO₆F₂ polyhedra. For RbPbCO₃F, infrared and ultraviolet–visible spectroscopy and thermogravimetric and differential thermal analysis measurements were performed. RbPbCO₃F is a new noncentrosymmetric material and crystallizes in the <i>achiral</i> and <i>nonpolar</i> space group <i>P</i>6̅<i>m</i>2 (crystal class 6̅<i>m</i>2). Powder second-harmonic generation (SHG) measurements on RbPbCO₃F and CsPbCO₃F using 1064 nm radiation revealed an SHG efficiency of approximately 250 and 300 × α-SiO₂, respectively. Charge constants <i>d</i>₃₃ of approximately 72 and 94 pm/V were obtained for RbPbCO₃F and CsPbCO₃F, respectively, through converse piezoelectric measurements. Electronic structure calculations indicate that the nonlinear optical response originates from the distorted PbO₆F₂ polyhedra, because of the even–odd parity mixing of the O 2<i>p</i> states with the nearly spherically symmetric 6<i>s</i> electrons of Pb²⁺. The degree of inversion symmetry breaking is quantified using a mode-polarization vector analysis and is correlated with cation size mismatch, from which it is possible to deduce the acentric properties of 3D alkali-metal fluorocarbonates

Phase-Matching in Nonlinear Optical Compounds: A Materials Perspective

Angle phase-matching in nonlinear optical (NLO) materials is critical for technological applications. The purpose of this manuscript is to describe the concept of phase-matching for the materials synthesis NLO community. Refractive index and birefringence are defined with respect to uniaxial and biaxial crystal systems. The phase-matching angle and wavelength range, Type I and Type II, are explained using real NLO materials, K₃B₆O₁₀Cl (KBOC) and Ba₃(ZnB₅O₁₀)­PO₄ (BZBP) In addition, we describe how refractive index measurements are performed on single crystals and how the resulting birefringence impacts the phase-matching. Our goal is to provide a description of phase-matching that is relevant for the materials synthesis NLO community

Deep-Ultraviolet Nonlinear-Optical Material K₃Sr₃Li₂Al₄B₆O₂₀F: Addressing the Structural Instability Problem in KBe₂BO₃F₂

A beryllium-free deep-ultraviolet (DUV) nonlinear-optical (NLO) material, K₃Sr₃Al₄Li₂B₆O₂₀F, has been synthesized and characterized. Unlike KBe₂BO₃F₂ (KBBF), the reported NLO material does not require the use of toxic BeO in the synthesis, and through the judicious selection of cations, strong interlayer interactions are observed that facilitate the crystal growth. K₃Sr₃Al₄Li₂B₆O₂₀F exhibits second-harmonic generation (SHG) at both 1064 and 532 nm with efficiencies of 1.7KH₂PO₄ and 0.3β-BaB₂O₄ and has an absorption edge of 190 nm. Because of the strong interlayer interactions, we were able to grow well-faceted large crystals, 8 × 8 × 5 mm³, through a top-seeded-solution-growth technique. With these crystals, we determined a birefringence of 0.0574 at 1064 nm and a type I phase-matching SHG limit of 224 nm