A5080034867- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Inorganic Chemistry and Materials
- Perovskite Materials and Applications
- Solid-state spectroscopy and crystallography
- Machine Learning in Materials Science
- Advanced Condensed Matter Physics
- Crystal Structures and Properties
- Iron-based superconductors research
- MXene and MAX Phase Materials
- Rare-earth and actinide compounds
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Metal and Thin Film Mechanics
- Multiferroics and related materials
- Organic and Molecular Conductors Research
- Thermal Expansion and Ionic Conductivity
- Layered Double Hydroxides Synthesis and Applications
- Quantum Dots Synthesis And Properties
- Phase-change materials and chalcogenides
- Polyoxometalates: Synthesis and Applications
- Metal-Organic Frameworks: Synthesis and Applications
- Magnetism in coordination complexes
- Crystallography and molecular interactions
- Catalysis and Oxidation Reactions
Colorado State University
2016-2025
Lawrence Berkeley National Laboratory
2023
Stony Brook University
2023
University of Minnesota
2023
University of California, Berkeley
2023
Brookhaven National Laboratory
2023
Johns Hopkins University
2011-2022
Color (United States)
2022
University of California, Santa Barbara
2009-2014
Collaborative Innovation Center of Quantum Matter
2014
In this work, we present our discovery and characterization of a new kagome prototype structure, ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$. We also the isostructural compounds ${\mathrm{RbV}}_{3}{\mathrm{Sb}}_{5}$ ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$. All materials exhibit structurally perfect two-dimensional net vanadium. Density-functional theory calculations indicate that are metallic, with Fermi level in close proximity to several Dirac points. Powder single-crystal syntheses presented,...
Vacancy-ordered double perovskites of the general formula A2BX6 are a family perovskite derivatives composed face-centered lattice nearly isolated [BX6] units with A-site cations occupying cuboctahedral voids. Despite presence octahedral units, close-packed iodide provides significant electronic dispersion, such that Cs2SnI6 has recently been explored for applications in photovoltaic devices. To elucidate structure-property relationships these materials, we have synthesized solid-solution...
Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature affects properties two-dimensional and devices is rarely reported. Here we demonstrate that selection (i.e., selective fluorination phenethylammonium) film perovskites, leading different device performance perovskite cells (average n = 4). Structural...
Halide perovskite semiconductors such as methylammonium lead iodide (CH3NH3PbI3) have achieved great success in photovoltaic devices; however, concerns surrounding toxicity of and material stability motivated the field to pursue alternative compositions structures. Vacancy-ordered double perovskites are a defect-ordered variant structure characterized by an antifluorite arrangement isolated octahedral units bridged A-site cations. In this Review, we focus upon structure–dynamics–property...
The advantageous performance of hybrid organic–inorganic perovskite halide semiconductors in optoelectronic applications motivates studies their fundamental crystal chemistry. In particular, recent have sought to understand how dipolar, dynamic, and organic cations such as methylammonium (CH3NH3+) formamidinium (CH(NH2)2+) affect physical properties light absorption charge transport. To probe the influence coupling on transport, we prepared series vacancy-ordered double derivatives A2SnI6,...
Lattice dynamics and structural instabilities are strongly implicated in dictating the electronic properties of perovskite halide semiconductors. We present a study vacancy-ordered double Rb2SnI6 correlate dynamic cooperative octahedral tilting with changes behavior compared to those Cs2SnI6. Though both compounds exhibit native n-type semiconductivity, exhibits carrier mobilities that reduced by factor ∼50 relative From synchrotron powder X-ray diffraction, we find adopts tetragonal...
We report long-range ordered antiferromagnetism concomitant with local iron displacements in the spin-ladder compound BaFe$_2$Se$_3$. Short-range magnetic correlations, present at room temperature, develop into antiferromagnetic order below T$_N$ = 256 K, no superconductivity down to 1.8 K. Built of ferromagnetic Fe$_4$ plaquettes, ground state correlates Fe atoms. These imply significant magnetoelastic coupling FeX$_4$-based materials, an ingredient hypothesized be important emergence...
The control of solid state reaction pathways will enable the design and discovery new functional inorganic materials. A range synthetic approaches have been used to shift chemistry away from thermodynamic control, in which most energetically favorable product forms, toward a regime kinetic so that metastable materials can be controllably produced. In this Perspective, we focus on metathesis reactions alter products. We provide insight into necessary components kinetically controlled...
Interest in inorganic ternary nitride materials has grown rapidly over the past few decades, as their diverse chemistries and structures make them appealing for a variety of applications. Due to synthetic challenges posed by stability N 2 , number predicted compounds dwarfs that been synthesized, offering breadth opportunity exploration. This review summarizes fundamental properties structural chemistry nitrides, leveraging metastability impact nitrogen chemical potential. A discussion...
The emission of white light from a single material is atypical and interest for solid-state lighting applications. Broadband has been observed in some layered perovskite derivatives, A2PbBr4 (A = R-NH3+), correlates with static structural distortions corresponding to out-of-plane tilting the lead bromide octahedra. While materials different organic cations can yield distinct tilts, underlying origin octahedral remains poorly understood. Using high energy resolution (e.g., quasi-elastic)...
Recent computational studies have predicted many new ternary nitrides, revealing synthetic opportunities in this underexplored phase space. However, synthesizing nitrides is difficult, part because intermediate and product phases often high cohesive energies that inhibit diffusion. Here, we report the synthesis of two phases, calcium zirconium nitride (CaZrN2) hafnium (CaHfN2), by solid state metathesis reactions between Ca3N2 MCl4 (M = Zr, Hf). Although reaction nominally proceeds to target...
Here we show that the 2.80(8)${\ensuremath{\mu}}_{\mathrm{B}}$ Fe${}^{\ensuremath{-}1}$ block antiferromagnetic order of BaFe${}_{2}$Se${}_{3}$ transforms into stripe in KFe${}_{2}$Se${}_{3}$ with a decrease moment to 2.1(1)${\ensuremath{\mu}}_{\mathrm{B}}$ Fe${}^{\ensuremath{-}1}$. This reduction is larger than expected from change electron count Ba${}^{2+}$ K${}^{+}$, and occurs loss displacements Fe atoms ideal positions ladders, as found by neutron pair distribution function analysis....
Inorganic materials with organic constituents-hybrid materials-have shown incredible promise as chemically tunable functional interesting optical and electronic properties. Here, the preparation structure are reported of two hybrid containing optoelectronically active tropylium ion within tin- lead-iodide inorganic frameworks distinct topologies. The crystal structures tin iodide, (C7H7)2SnI6, lead C7H7PbI3, were solved using high-resolution synchrotron powder X-ray diffraction informed by...
High-temperature superconductivity has a range of applications from sensors to energy distribution. Recent reports this phenomenon in compounds containing electronically active BiS2 layers have the potential open new chapter field superconductivity. Here we report identification and basic properties two ternary Bi-O-S compounds, Bi2OS2 Bi3O2S3. The former is non-superconducting; latter likely explains at T(c) = 4.5 K previously reported "Bi4O4S3". Bi3O2S3 found be sensitive number...
Based on specific heat and magnetoresistance measurements, we report that a "heavy" electronic state exists below $T \approx$ 20 K in KNi$_2$Se$_2$, with an increased carrier mobility enhanced effective band mass, $m$* = 6$m_b$ to 18$m_b$. This evolves into superconductivity at $T_c$ 0.80(1) K. These properties resemble of many-body heavy-fermion state, which derives from the hybridization between localized magnetic states conduction electrons. Yet, no evidence for magnetism or order is...
Two-dimensional (2D) organic–inorganic hybrid perovskites (OIHPs) have showed impressive stability, compared to their three-dimensional (3D) counterparts. However, tuning the chemical structure of organic cations simultaneously improve device performance and stability 2D OIHP solar cells is rarely reported. Here, we demonstrate that by introducing a classic noncovalent aryl-perfluoroaryl interaction, with 1:1 mixed phenethylammonium (PEA) perfluorophenethylammonium (F5-PEA) can achieve an...
Low-spin (<italic>S</italic> = 1/2) Ni(<sc>iii</sc>) cyclam complex salts can show SMM-type properties depending on the axial ligand donor atom identity.
Although initial studies on hybrid perovskites for photovoltaic applications focused simple compositions, the most technologically relevant are heavily substituted. The influence of chemical substitution general phase behavior and specific physical properties remains ambiguous. perovskite formamidinium lead bromide, CH(NH2)2PbBr3, exhibits complex manifesting in a series crystallographically unresolvable transitions associated with changes cation dynamics. Here, we characterize molecular...
Using an analytical theory, experimental terahertz time-domain spectroscopy data and numerical evidence, we demonstrate that the frequency dependence of absorption coupling coefficient between far-infrared photons atomic vibrations in disordered materials has universal functional form, C(omega) = A + B*omega^2, where material-specific constants B are related to distributions fluctuating charges obeying global local charge neutrality, respectively.
Iron pnictides and selenides display a variety of unusual magnetic phases originating from the interplay between electronic, orbital, lattice degrees freedom. Using powder inelastic neutron scattering on two-leg ladder BaFe2Se3, we fully characterize static dynamic spin correlations associated with Fe4 block state, an exotic ground state observed in this low-dimensional magnet Rb0.89Fe1.58Se2. All excitations predicted by effective Heisenberg model localized spins are below 300 meV...
Solid-state diffusion is often the primary limitation in synthesis of crystalline inorganic materials and prevents potential discovery isolation new that may not be most stable with respect to reaction conditions. Synthetic approaches circumvent solid-state reactions are rare allow formation metastable products. To this end, we present an situ study metathesis MCl2 + Na2S2 → MS2 2 NaCl (M = Fe, Co, Ni) using synchrotron powder X-ray diffraction differential scanning calorimetry. Depending on...
Hybrid organic–inorganic perovskites have gained notoriety in the photovoltaic community for their composition-tunable band gaps and long-lived electronic excited states, which are known to be related crystalline phase. While it is that inorganic organic components coupled through structural phase transitions, remains unclear as what role each plays directing structure of hybrid such methylammonium lead halides (CH3NH3PbX3). Here, we present crystallographic spectroscopic data series...
The synthesis of complex oxides requires high temperatures to overcome barriers imparted by solid-state diffusion; as such, reactions typically yield the most stable polymorph for a given composition. To synthesize new or metastable oxides, kinetically competent with lower initial energy must be devised control reaction pathway and resulting products. This contribution details selective different yttrium manganese through assisted metathesis between Mn2O3, YCl3, A2CO3 under flowing oxygen;...
In sharp contrast to molecular synthesis, materials synthesis is generally presumed lack selectivity. The few known methods of designing selectivity in solid-state reactions have limited scope, such as topotactic or strain stabilization. This contribution describes a general approach for searching large chemical spaces identify selective reactions. novel explains the ability nominally "innocent" Na2CO3 precursor enable metathesis single-phase Y2Mn2O7: an outcome that was previously only...