Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
High-pressure-induced comminution and recrystallization of CH3NH3PbBr3 nanocrystals as large thin... more High-pressure-induced comminution and recrystallization of CH3NH3PbBr3 nanocrystals as large thin nanoplates
Journal of materials chemistry. A, Materials for energy and sustainability, 2015
A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance st... more A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance study of the hybrid perovskites CH3NH3PbX3 (X = I, Br and Cl)
Fluor-chlorellestadite solid solutions Ca 10 (SiO 4) 3 (SO 4) 3 Cl 2−x F x , serving as prototype... more Fluor-chlorellestadite solid solutions Ca 10 (SiO 4) 3 (SO 4) 3 Cl 2−x F x , serving as prototype crystalline matrices for the fixation of hazardous fly ash, were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The lattice parameters of the ellestadites vary linearly with composition and show the expected shrinkage of unit cell volume as fluorine (IR = 1.33 Å) displaces chlorine (IR = 1.81 Å). FTIR spectra indicate little or no OH − in the solid solutions. All compositions conform to P6 3 / m symmetry where F − is located at the 2a (0, 0, 1 / 4) position, while Cl − is displaced out of the 6h Ca(2) triangle plane and occupies 4e (0, 0, z) split positions with z ranging from 0.336(3) to 0.4315(3). Si/S randomly occupy the 6h tetrahedral site. Ellestadites rich in Cl (x ≤ 1.2) show an overall deficiency in halogens (<2 atom per formula unit), particularly Cl as a result of CaCl 2 volatilization, with charge balance achieved by the creation of Ca vacancies (Ca 2+ + 2Cl − →□ Ca + 2□ Cl) leading to the formula Ca 10−y (SiO 4) 3 (SO 4) 3 Cl 2−x−2y F x. For F-rich compositions the vacancies are found at Ca(2), while for Cl-rich ellestadites, vacancies are at Ca(1). It is likely the loss of CaCl 2 which leads tunnel anion vacancies promotes intertunnel positional disorder, preventing the formation of a P2 1 /b monoclinic dimorph, analogous to that reported for Ca 10 (PO 4) 6 Cl 2. Trends in structure with composition were analyzed using crystal-chemical parameters, whose systematic variations served to validate the quality of the Rietveld refinements. 65 rellestadites are regarded as isostructural, although the halides 66 reside at different locations along the c-axis anion tunnels. In 67 the synthetic fluorellestadite (P6 3 /m) endmember, F − at (0, 0, 68 1/4 and 0, 0, 3 / 4) lies in the center of a Ca(2) triangle on the 69 mirror planes at z = 1/4 and z = 3 / 4. 12 In the corresponding 70 chlorellestadite endmember, Cl − cannot fit into the Ca(2) 71 triangle (ionic radii for VI F − = 1.33 Å and VI Cl − = 1.81 Å 13), 72 and statistically occupies (0, 0, z) sites, ∼1.1 Å above or below 73 the mirror plane. 9 In the case of natural hydroxyellestadite, 74 Sudarsanan 7 refined separate sites for OH − (0, 0, 0.2033), F − 75 (0, 0, 1 / 4), and Cl − (0, 0, 0.3644) in P2 1 /m with site 76 occupancies of 0.806(9), 0.15(6), and 0.092(5) respectively.
The ellestadite apatites Ca 10 [(SiO 4) x (PO 4) 6−2x (SO 4) x ]Cl 2 were studied by powder X-ray... more The ellestadite apatites Ca 10 [(SiO 4) x (PO 4) 6−2x (SO 4) x ]Cl 2 were studied by powder X-ray and neutron diffraction to establish baseline crystallographic data. These synthetic materials, unlike mineral specimens that are well equilibrated, show no Si/P/S ordering and conform to P6 3 /m symmetry. Phosphate-rich ellestadites where 0 ≤ x ≤ 1 show chemical stability towards Toxicity Characterization Leaching Procedure (TCLP) testing and are potential immobilization matrices for mixed toxic metal wastes.
Journal of the American Chemical Society, Dec 18, 2018
Resolving the structure−property relationships of twodimensional (2D) organic−inorganic hybrid pe... more Resolving the structure−property relationships of twodimensional (2D) organic−inorganic hybrid perovskites is essential for the development of photovoltaic and photoelectronic devices. Here, pressure (0−10 GPa) was applied to 2D hybrid perovskite flakes mechanically exfoliated from butylammonium lead halide single crystals, (C 4 H 9 NH 3) 2 PbI 4 , from which we observed a series of changes of the strong excitonic emissions in the photoluminescence spectra. By correlating with in situ high-pressure X-ray diffraction results, we examine successfully the relationship between structural modifications in the inorganic PbI 4 2− layer and their excitonic properties. During the transition between Pbca (1b) phase and Pbca (1a) phase at around 0.1 GPa, the decrease in ⟨Pb−I−Pb⟩ bond angle and increase in Pb−I bond length lead to an abrupt blue shift of the excitonic bandgap. The presence of the P2 1 /a phase above 1.4 GPa increases the ⟨Pb−I−Pb⟩ bond angle and decreases the Pb−I bond length, leading to a deep red shift of the excitonic bandgap. The total band gap narrowing of ∼350 meV to 2.03 eV at 5.3 GPa before amorphization, facilitates (C 4 H 9 NH 3) 2 PbI 4 as a much better solar absorber. Moreover, phase transitions inevitably modify the carrier lifetime of (C 4 H 9 NH 3) 2 PbI 4 , where an initial 150 ps at ambient phase is prolongated to 190 ps in the Pbca (1a) phase along with enhanced photoluminescence (PL), originating from pressure-induced strong radiative recombination of trapped excitons.The onset of P2 1 /a phase shortens significantly the carrier lifetime to 53 ps along with a weak PL emission due to pressure-induced severe lattice distortion and amorphization. High-pressure study on (C 4 H 9 NH 3) 2 PbI 4 nm-thin flakes may provide insights into the mechanisms for synthetically designing novel 2D hybrid perovskite based photoelectronic devices and solar cells.
Mechanochemically synthesized dual cation hybrid perovskites of the form (CsxMA1−x)Pb(Cl/Br)3 (x ... more Mechanochemically synthesized dual cation hybrid perovskites of the form (CsxMA1−x)Pb(Cl/Br)3 (x = 0–1) exhibit complete miscibility and high structural order across each compositional range.
Potassium substituted double perovskite nanocrystals of the form Cs2KxAg1−xInCl6:Bi (x= 0–1) exhi... more Potassium substituted double perovskite nanocrystals of the form Cs2KxAg1−xInCl6:Bi (x= 0–1) exhibit improved PLQY behaviour and structural diversity.
Structural and optical properties of MAxCs1−xPbBr3 mixed cation colloidal nanoparticles with 13 m... more Structural and optical properties of MAxCs1−xPbBr3 mixed cation colloidal nanoparticles with 13 mol% Cs composition exhibiting the longest charge carrier lifetime and enhancement in radiative pathways.
Demonstration of Rb2CuX3 (X = Br, Cl) colloidal nanocrystals under UV light with a representation... more Demonstration of Rb2CuX3 (X = Br, Cl) colloidal nanocrystals under UV light with a representation of one-dimensional Rb2CuBr3 crystal structure.
Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8)... more Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8) was prepared by solid-state and wet chemical processing to explore the impact of the synthesis route and mode of crystal chemical incorporation of copper on the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains. Apatites prepared by solid-state reaction showed unit cell volume dilation from 527.17 Å3 for copper-free HA to 533.31 Å3 for material of the putative composition Ca10(PO4)6[Cu0.8(OH)0.4O0.8] consistent with Cu+ insertion into the [001] hydroxyapatite channel. This was less pronounced (528.30 Å3 to 529.3 Å3) in the corresponding wet chemical synthesised products, suggesting less complete Cu tunnel incorporation and partial tenancy of Cu in place of calcium. X-ray absorption spectroscopy suggests fast quenching is necessary to prevent oxidation of Cu+ to Cu2+. Raman spectroscopy revealed an absorption band at 630 cm−1 characte...
ABSTRACTPressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylam... more ABSTRACTPressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laser-excited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tun...
Where a licence is displayed above, please note the terms and conditions of the licence govern yo... more Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.
Advanced materials (Deerfield Beach, Fla.), Jan 27, 2017
High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS ... more High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (...
Hydrogen-bonding exists in all hybrid organic-inorganic lead halide perovskites MAPbX 3 (X = Cl, ... more Hydrogen-bonding exists in all hybrid organic-inorganic lead halide perovskites MAPbX 3 (X = Cl, Br, I). It has great influence on the structure, stability, electronic and optical properties of such perovskite family. The hydrogen-bonding state between the H atoms of the methylammonium (MA) cation and the halide ions is resolved by combining ab initio calculations with temperature-dependent Raman scattering and powder X-ray diffraction (XRD) measurements on MAPbBr 3 hybrid perovskites. Upon cooling, the H-bonding in the NH 3 end of the MA group shows sequential changes while the H atoms in the CH 3 end only form H bonds with the Br ions in the orthorhombic phase, leading to a reduction in the rotational freedom of MA and a narrowing for MA Raman modes. The hydrogen-bonding drives the evolution of temperature-dependent rotations of MA cation and the concomitant tilting of PbX 6 octahedra with the consequent dynamical change of the electronic band structures, from indirect bandgap to direct bandgap along with PL emission enhancement of ~ 60 times upon cooling. We experimentally and theoretically reveal the evolution of hydrogen-bonding during polymorphic transformations, the different types of hydrogenbonding lead to specific optoelectronic properties and device applications of hybrid perovskites.
It is shown that a crystalline metal−organic framework (HKUST-1) can be rapidly synthesized from ... more It is shown that a crystalline metal−organic framework (HKUST-1) can be rapidly synthesized from a DMSO/MeOH solution with greatly reduced amounts of organic solvents using a supercritical CO 2 (scCO 2) solvent expansion technique. The precursor solution is stable for months under ambient conditions, and CO 2-driven MOF (metal−organic framework) crystallization is achieved under mild conditions (40°C, 40−100 bar) with excellent reproducibility. As the degree of liquid-phase expansion drives MOF nucleation and growth, the crystallite size and overall yield can be tuned by adjusting the CO 2 pressure. Furthermore, scanning electron microscopy (SEM), highresolution transmission electron microscopy (HR-TEM), and gas sorption analyses showed that, in the presence of scCO 2 , HKUST-1 crystallites with a hierarchical pore structure are generated through a postcrystallization etching process. These findings demonstrate that scCO 2 is a time-and material-efficient route to MOF synthesis with a high level of control over the crystallization process for accessing tailored material properties.
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
High-pressure-induced comminution and recrystallization of CH3NH3PbBr3 nanocrystals as large thin... more High-pressure-induced comminution and recrystallization of CH3NH3PbBr3 nanocrystals as large thin nanoplates
Journal of materials chemistry. A, Materials for energy and sustainability, 2015
A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance st... more A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance study of the hybrid perovskites CH3NH3PbX3 (X = I, Br and Cl)
Fluor-chlorellestadite solid solutions Ca 10 (SiO 4) 3 (SO 4) 3 Cl 2−x F x , serving as prototype... more Fluor-chlorellestadite solid solutions Ca 10 (SiO 4) 3 (SO 4) 3 Cl 2−x F x , serving as prototype crystalline matrices for the fixation of hazardous fly ash, were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The lattice parameters of the ellestadites vary linearly with composition and show the expected shrinkage of unit cell volume as fluorine (IR = 1.33 Å) displaces chlorine (IR = 1.81 Å). FTIR spectra indicate little or no OH − in the solid solutions. All compositions conform to P6 3 / m symmetry where F − is located at the 2a (0, 0, 1 / 4) position, while Cl − is displaced out of the 6h Ca(2) triangle plane and occupies 4e (0, 0, z) split positions with z ranging from 0.336(3) to 0.4315(3). Si/S randomly occupy the 6h tetrahedral site. Ellestadites rich in Cl (x ≤ 1.2) show an overall deficiency in halogens (<2 atom per formula unit), particularly Cl as a result of CaCl 2 volatilization, with charge balance achieved by the creation of Ca vacancies (Ca 2+ + 2Cl − →□ Ca + 2□ Cl) leading to the formula Ca 10−y (SiO 4) 3 (SO 4) 3 Cl 2−x−2y F x. For F-rich compositions the vacancies are found at Ca(2), while for Cl-rich ellestadites, vacancies are at Ca(1). It is likely the loss of CaCl 2 which leads tunnel anion vacancies promotes intertunnel positional disorder, preventing the formation of a P2 1 /b monoclinic dimorph, analogous to that reported for Ca 10 (PO 4) 6 Cl 2. Trends in structure with composition were analyzed using crystal-chemical parameters, whose systematic variations served to validate the quality of the Rietveld refinements. 65 rellestadites are regarded as isostructural, although the halides 66 reside at different locations along the c-axis anion tunnels. In 67 the synthetic fluorellestadite (P6 3 /m) endmember, F − at (0, 0, 68 1/4 and 0, 0, 3 / 4) lies in the center of a Ca(2) triangle on the 69 mirror planes at z = 1/4 and z = 3 / 4. 12 In the corresponding 70 chlorellestadite endmember, Cl − cannot fit into the Ca(2) 71 triangle (ionic radii for VI F − = 1.33 Å and VI Cl − = 1.81 Å 13), 72 and statistically occupies (0, 0, z) sites, ∼1.1 Å above or below 73 the mirror plane. 9 In the case of natural hydroxyellestadite, 74 Sudarsanan 7 refined separate sites for OH − (0, 0, 0.2033), F − 75 (0, 0, 1 / 4), and Cl − (0, 0, 0.3644) in P2 1 /m with site 76 occupancies of 0.806(9), 0.15(6), and 0.092(5) respectively.
The ellestadite apatites Ca 10 [(SiO 4) x (PO 4) 6−2x (SO 4) x ]Cl 2 were studied by powder X-ray... more The ellestadite apatites Ca 10 [(SiO 4) x (PO 4) 6−2x (SO 4) x ]Cl 2 were studied by powder X-ray and neutron diffraction to establish baseline crystallographic data. These synthetic materials, unlike mineral specimens that are well equilibrated, show no Si/P/S ordering and conform to P6 3 /m symmetry. Phosphate-rich ellestadites where 0 ≤ x ≤ 1 show chemical stability towards Toxicity Characterization Leaching Procedure (TCLP) testing and are potential immobilization matrices for mixed toxic metal wastes.
Journal of the American Chemical Society, Dec 18, 2018
Resolving the structure−property relationships of twodimensional (2D) organic−inorganic hybrid pe... more Resolving the structure−property relationships of twodimensional (2D) organic−inorganic hybrid perovskites is essential for the development of photovoltaic and photoelectronic devices. Here, pressure (0−10 GPa) was applied to 2D hybrid perovskite flakes mechanically exfoliated from butylammonium lead halide single crystals, (C 4 H 9 NH 3) 2 PbI 4 , from which we observed a series of changes of the strong excitonic emissions in the photoluminescence spectra. By correlating with in situ high-pressure X-ray diffraction results, we examine successfully the relationship between structural modifications in the inorganic PbI 4 2− layer and their excitonic properties. During the transition between Pbca (1b) phase and Pbca (1a) phase at around 0.1 GPa, the decrease in ⟨Pb−I−Pb⟩ bond angle and increase in Pb−I bond length lead to an abrupt blue shift of the excitonic bandgap. The presence of the P2 1 /a phase above 1.4 GPa increases the ⟨Pb−I−Pb⟩ bond angle and decreases the Pb−I bond length, leading to a deep red shift of the excitonic bandgap. The total band gap narrowing of ∼350 meV to 2.03 eV at 5.3 GPa before amorphization, facilitates (C 4 H 9 NH 3) 2 PbI 4 as a much better solar absorber. Moreover, phase transitions inevitably modify the carrier lifetime of (C 4 H 9 NH 3) 2 PbI 4 , where an initial 150 ps at ambient phase is prolongated to 190 ps in the Pbca (1a) phase along with enhanced photoluminescence (PL), originating from pressure-induced strong radiative recombination of trapped excitons.The onset of P2 1 /a phase shortens significantly the carrier lifetime to 53 ps along with a weak PL emission due to pressure-induced severe lattice distortion and amorphization. High-pressure study on (C 4 H 9 NH 3) 2 PbI 4 nm-thin flakes may provide insights into the mechanisms for synthetically designing novel 2D hybrid perovskite based photoelectronic devices and solar cells.
Mechanochemically synthesized dual cation hybrid perovskites of the form (CsxMA1−x)Pb(Cl/Br)3 (x ... more Mechanochemically synthesized dual cation hybrid perovskites of the form (CsxMA1−x)Pb(Cl/Br)3 (x = 0–1) exhibit complete miscibility and high structural order across each compositional range.
Potassium substituted double perovskite nanocrystals of the form Cs2KxAg1−xInCl6:Bi (x= 0–1) exhi... more Potassium substituted double perovskite nanocrystals of the form Cs2KxAg1−xInCl6:Bi (x= 0–1) exhibit improved PLQY behaviour and structural diversity.
Structural and optical properties of MAxCs1−xPbBr3 mixed cation colloidal nanoparticles with 13 m... more Structural and optical properties of MAxCs1−xPbBr3 mixed cation colloidal nanoparticles with 13 mol% Cs composition exhibiting the longest charge carrier lifetime and enhancement in radiative pathways.
Demonstration of Rb2CuX3 (X = Br, Cl) colloidal nanocrystals under UV light with a representation... more Demonstration of Rb2CuX3 (X = Br, Cl) colloidal nanocrystals under UV light with a representation of one-dimensional Rb2CuBr3 crystal structure.
Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8)... more Copper-doped hydroxyapatite (HA) of nominal composition Ca10(PO4)6[Cux(OH)2-2xOx] (0.0 ≤ x ≤ 0.8) was prepared by solid-state and wet chemical processing to explore the impact of the synthesis route and mode of crystal chemical incorporation of copper on the antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains. Apatites prepared by solid-state reaction showed unit cell volume dilation from 527.17 Å3 for copper-free HA to 533.31 Å3 for material of the putative composition Ca10(PO4)6[Cu0.8(OH)0.4O0.8] consistent with Cu+ insertion into the [001] hydroxyapatite channel. This was less pronounced (528.30 Å3 to 529.3 Å3) in the corresponding wet chemical synthesised products, suggesting less complete Cu tunnel incorporation and partial tenancy of Cu in place of calcium. X-ray absorption spectroscopy suggests fast quenching is necessary to prevent oxidation of Cu+ to Cu2+. Raman spectroscopy revealed an absorption band at 630 cm−1 characte...
ABSTRACTPressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylam... more ABSTRACTPressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laser-excited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tun...
Where a licence is displayed above, please note the terms and conditions of the licence govern yo... more Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.
Advanced materials (Deerfield Beach, Fla.), Jan 27, 2017
High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS ... more High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (...
Hydrogen-bonding exists in all hybrid organic-inorganic lead halide perovskites MAPbX 3 (X = Cl, ... more Hydrogen-bonding exists in all hybrid organic-inorganic lead halide perovskites MAPbX 3 (X = Cl, Br, I). It has great influence on the structure, stability, electronic and optical properties of such perovskite family. The hydrogen-bonding state between the H atoms of the methylammonium (MA) cation and the halide ions is resolved by combining ab initio calculations with temperature-dependent Raman scattering and powder X-ray diffraction (XRD) measurements on MAPbBr 3 hybrid perovskites. Upon cooling, the H-bonding in the NH 3 end of the MA group shows sequential changes while the H atoms in the CH 3 end only form H bonds with the Br ions in the orthorhombic phase, leading to a reduction in the rotational freedom of MA and a narrowing for MA Raman modes. The hydrogen-bonding drives the evolution of temperature-dependent rotations of MA cation and the concomitant tilting of PbX 6 octahedra with the consequent dynamical change of the electronic band structures, from indirect bandgap to direct bandgap along with PL emission enhancement of ~ 60 times upon cooling. We experimentally and theoretically reveal the evolution of hydrogen-bonding during polymorphic transformations, the different types of hydrogenbonding lead to specific optoelectronic properties and device applications of hybrid perovskites.
It is shown that a crystalline metal−organic framework (HKUST-1) can be rapidly synthesized from ... more It is shown that a crystalline metal−organic framework (HKUST-1) can be rapidly synthesized from a DMSO/MeOH solution with greatly reduced amounts of organic solvents using a supercritical CO 2 (scCO 2) solvent expansion technique. The precursor solution is stable for months under ambient conditions, and CO 2-driven MOF (metal−organic framework) crystallization is achieved under mild conditions (40°C, 40−100 bar) with excellent reproducibility. As the degree of liquid-phase expansion drives MOF nucleation and growth, the crystallite size and overall yield can be tuned by adjusting the CO 2 pressure. Furthermore, scanning electron microscopy (SEM), highresolution transmission electron microscopy (HR-TEM), and gas sorption analyses showed that, in the presence of scCO 2 , HKUST-1 crystallites with a hierarchical pore structure are generated through a postcrystallization etching process. These findings demonstrate that scCO 2 is a time-and material-efficient route to MOF synthesis with a high level of control over the crystallization process for accessing tailored material properties.
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