Principles Density Functional Theory Research Articles

The structural, stability, electronic, optical and thermodynamic properties of Ba2AsXO6（X = V, Nb, Ta）double perovskite oxides: A First-Principles study

In this paper, the structural, mechanical, electronic, optical and thermodynamic properties of Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have been studied based on the first principles of density functional theory. By calculating some parameters such as Goldsmith’s tolerance factor (tG), octahedral factor (µ), Bartel’s tolerance factor (τ), formation energy, binding energy and elastic constants, it is found that these double perovskite oxides have the potential for stable existence. In addition, Ba2AsXO6 (X = V, Nb, Ta) is an anisotropic material, in which Ba2AsVO6 is brittle, Ba2AsNbO6 and Ba2AsTaO6 are ductile. The electronic properties of the materials show that Ba2AsVO6 and Ba2AsNbO6 are indirect bandgap semiconductors with a band gap of 1.676 eV and 2.654 eV respectively, while Ba2AsTaO6 is direct bandgap semiconductor with a band gap of 3.252 eV. The optical properties revealed that these perovskites exhibit favorable far-ultraviolet light absorption characteristics. The thermodynamic properties show that the specific heat capacity of these double perovskite oxides reaches the Dulong-Petit limit at around 800 K. These results indicate that Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have broad application prospects in the fields of thermoelectricity and optoelectronics. Furthermore, these results also provide a valuable theoretical basis for their future experimental synthesis.

First principles modelling of the ion binding capacity of finger millet

Finger millet, a cereal grain widely consumed in India and Africa, has gained more attention in recent years due to its high dietary fibre (arabinoxylan) and trace mineral content, and its climate resilience. The aim of this study was to understand the interactions between potassium (K+), calcium (Ca2+) and zinc (Zn2+) ions and the arabinoxylan structure and determine its ion-binding capacity. Three variations of a proposed model of the arabinoxylan structure were constructed and first principles Density Functional Theory calculations were carried out to determine the cation-binding capacity of the arabinoxylan complexes. Zn2+-arabinoxylan complexes were highly unstable and thermodynamically unfavourable in all three models. Ca2+ and K+ ions, however, form thermodynamically stable complexes, particularly involving two glucuronic acid residues as a binding pocket. Glucuronic acid residues are found to play a key role in stabilising the cation-arabinoxylan complex, and steric effects are more important to the stability than charge density. Our results highlight the most important structural features of the millet fibre regarding ion-storage capacity, and provide valuable preliminary data for confirmatory experimental studies and for the planning of clinical trials where the bioavailability of bound ions following digestion may be tested.

Emerging topological states in EuMn2Bi2: A first principles prediction

New materials with magnetic order driven topological phases are hugely sought after for their immense application potential. In this work, we propose a new compound EuMn2Bi2 from our first principles density functional theory calculations to host novel topological phases such as Dirac/Weyl semimetal and topological insulator in its different magnetic states which are energetically close to one another. The new compound EuMn2Bi2 is found to be dynamically stable from our phonon calculations supporting its experimental preparation in future. By comparing the total energies of various possible magnetic structures of EuMn2Bi2, we identified the ground state. The magnetic ground state is found to be a normal insulator with tiny band gap which is an order of magnitude less than the same in another well studied sister compound EuMn2As2. However, there exist other magnetic states energetically very close to the ground state in EuMn2Bi2 which display remarkable non-trivial band topology such as Dirac/Weyl points close to the Fermi level and topological insulator state driven by magnetic order which is not observed in EuMn2As2. The energetic proximity of these magnetic order driven topological phases makes them tunable via external handle such as magnetic field indicating that the proposed new material EuMn2Bi2 would be a very versatile magnetic topological material if prepared experimentally in future.

Effect of non metallic doping in GeC gas sensors on gas response performance: the first principles study

In this paper, the stability, electronic structure and optical properties of monolayer GeC, B, N and P doped GeC systems are systematically investigated based on the first principles of density functional theory. The results show that the results show that the intrinsic GeC monolayer has a weak adsorption capacity for CH4 and C2H2, which is unfavourable for the sensing and trapping of CH4 and C2H2 gases. Based on calculated adsorption distance, adsorption energy and charge transfer, we find that P-GeC monolayer is the most sensitive to CH4 and C2H2 molecules, and the most of gas molecules act as acceptors to gain electrons from GeC monolayer. The adsorption energy of CH4 is smaller than that of C2H2 gas molecule, which implies that C2H2 is more easily desorbed from P-GeC. Moreover, the work function changes significantly when gas molecules adsorbed on B, N, P-GeC, and Recovery times indicate that B, N and P doped GeC monolayers are more selective and sensitive to C2H2 molecules compared to CH4 molecules. The research work aims to provide a theoretical basis for the application of GeC-based gas sensors, and P-doped GeC monolayers can be used as candidate materials for C2H2 gas sensing and trapping.

Ab-initio study of potassium-based halide perovskites for photovoltaic and opto-electronic applications

A first principle Density Functional Theory (DFT) analysis was applied to investigate the structural, electronic, and optical properties of cubic perovskites KXB3 (X= Ge, Sn; B= Cl, Br). Using the computational code WIEN2K, the corresponding properties have been studied through the use of Generalized Gradient Approximation. Experimental values of lattice constants are consistent with those derived from calculations. The wide direct band gap of 1.5–2 eV (M-M) is confirmed by the electronic band structure. This behavior suggests that the compounds under study are semiconducting KXB3 (X= Ge, Sn; B= Cl, Br) halide perovskite materials are a promising alternative to photovoltaic semiconductors because of their appealing optical properties, as confirmed by a variety of optical properties. Because of their advancement in perovskites, these materials can captivate the world. So, these perovskites materials can captivate world due to its advancement in Opto-electronic application especially in photovoltaic area.

Single atom dispersed tungsten disulfide (WS2) based nanosensors for VOCs detection related to decomposed humans in disaster events

Locating and recovering the victims as a result of disaster events is extremely challenging due to vast search areas, hazardous nature of destroyed infrastructure, and large number of potential victims. An effective avenue for the victim’s detection is through the sensing of human-specific volatile organic compounds (VOCs) emitted both in life and in death. Motivated by this, we employed first principles density functional theory (DFT) calculations to study the sensing properties of pristine, vacancy-induced and single atom dispersed tungsten disulfide (WS2) monolayers towards 11 specific VOCs associated with decomposing humans. We found that pristine, and vacancy-induced WS2 weakly adsorbed the selected VOCs with adsorption energies (Eads) between −0.26 to −0.76 eV. However, the incorporation of selected single atoms of Co, Fe, Nb, and Ni in WS2 improved the sensing properties tremendously. In particular, Nb-WS2 adsorbed the incident VOCs with Eads values of −1.89, −209, −1.43, −0.94, −2.08, −1.57, −1.44, −1.47, −1.70, −1.03, and −2.14 eV for 2-Butanone, benzaldehyde, butanol, heptane, hexanal, methylamine, dimethyl disulfide, dimethyl trisulfide, pyridine, octane, and toluene, respectively, which are ideal for efficient sensing mechanism. Appropriate adsorptions were coupled with the measurable changes in the electronic properties (band gaps) of Nb-WS2, which is essential for proficient sensing. Charge transfer analysis, electro localization functions, electrostatic potentials, and work function calculations further authenticated the sensing propensities of single atom dispersed WS2. Finally, Langmuir adsorption model was employed to explore the sensing at diverse pressure and temperature settings. We believe that these results will help for the development of highly efficient nanosensors for the detection of VOCs related to decomposed humans in mass disaster events. This will increase the detection ability and the chance of locating these victims.

Effects of Alloying Element on Hydrogen Adsorption and Diffusion on α-Fe(110) Surfaces: First Principles Study

Based on first principles density functional theory (DFT) methods, this study employed the Cambridge Serial Total Energy Package (CASTEP) module within Materials Studio (MS) software under the generalized gradient approximation to investigate the adsorption, diffusion behavior, and electronic properties of hydrogen atoms on α-Fe(110) and α-Fe(110)-Me (Mn, Cr, Ni, Mo) surfaces, including calculations of their adsorption energies and density of states (DOS). The results demonstrated that doping with alloy atoms Me increased the physical adsorption energy of H2 molecules on the surface. Specifically, Mo doping elevated the adsorption energy from −1.00825 eV to −0.70226 eV, with the largest relative change being 30.35%. After doping with Me, the chemical adsorption energy of two hydrogen atoms does not change significantly, among which doping with Cr results in a decrease in the chemical adsorption energy. Building on this, further analysis of the chemical adsorption of single atoms on the surface was conducted. By comparing the adsorption energy and the bond length between a hydrogen atom and iron/dopant metal atom, it was found that Mo doping has the greatest impact, increasing the bond length by 58.58%. Analysis of the DOS functions under different doping conditions validated the interaction between different alloy elements and H atoms. Simultaneously, simulations were carried out on the energy barrier crossed by H atoms diffusing into the metal interior. The results indicate that Ni doping facilitates the diffusion of H atoms, while Cr, Mn, and Mo hinder their diffusion, with Mo having the most significant effect, where its barrier is 21.88 times that of the undoped surface. This conclusion offers deep insights into the impact of different doping elements on hydrogen adsorption and diffusion, aiding in the design of materials resistant to hydrogen embrittlement.

A comparative study of NH3 and H2S sensing performance on monolayer nanosheets through first-principle studies

This study investigates the sensing of H2S and NH3 over 2D nanosheets, namely graphene (GRA), boron nitride (BN), silicon carbide (SiC) and boron carbon nitride (BCN), using the first principle density functional theory. A CAM-B3LYP/6–31 G level of theory was used for all the computations and evaluation of the geometric and electronic properties. The optimized clusters indicated the chemisorption between the gas molecules and the SiC nanosheet. The Fourier transform infrared (FTIR) spectra were obtained to study the N-H and S-H shifts in the post-adsorption clusters. Based on the magnitude of the computed adsorption energies, SiC (-0.61 eV for the H2S cluster and −1.21 eV for the NH3 cluster) was found to adsorb both the gas molecules most effectively. The electrostatic potential maps and the molecular orbitals' distribution were studied to investigate the electronic properties. The analysis showed that the adsorption of H2S and NH3 over GRA, BN, and BCN was physical, whereas, on SiC, nanosheet chemisorption was observed. Atom-In-Molecule (AIM) analysis was carried out to account for the possible weak interactions. The study concluded that the SiC nanosheet was the most suitable for the adsorption of H2S and NH3 gases.

Ultrafast Shift Current in SnS2 Single Crystals: Structure Considerations, Modeling, and THz Emission Spectroscopy

AbstractAbove‐band gap optical excitation of non‐centrosymmetric semiconductors can lead to the spatial shift of the center of electron charge in a process known as shift current. Shift current is investigated in single‐crystal SnS2, a layered semiconductor with the band gap of ≈2.3 eV, by THz emission spectroscopy and first principles density functional theory (DFT). It is observed that normal incidence excitation with above gap (400 nm; 3.1 eV) pulses results in THz emission from 2H SnS2 () polytype, where such emission is nominally forbidden by symmetry. It is argued that the underlying symmetry breaking arises due to the presence of stacking faults that are known to be ubiquitous in SnS2 single crystals and construct a possible structural model of a stacking fault with symmetry properties consistent with the experimental observations. In addition to shift current, it is observed THz emission by optical rectification excited by below band gap (800 nm; 1.55 eV) pulses but it requires excitation fluence more than two orders of magnitude higher to produce same signal amplitude. These results suggest that ultrafast shift current in which can be excited with visible light in blue–green portion of the spectrum makes SnS2 a promising source material for THz photonics.

First principles study of electronic structure and transport in graphene grain boundaries

Grain boundaries play a major role for electron transport in graphene sheets grown by chemical vapor deposition. Here we investigate the electronic structure and transport properties of idealized graphene grain boundaries (GBs) in bi-crystals using first principles density functional theory (DFT) and non-equilibrium Greens functions. We generated 150 different grain boundaries using an automated workflow where their geometry is relaxed with DFT. We find that the GBs generally show a quasi-1D bandstructure along the GB. We group the GBs in four classes based on their conductive properties: transparent, opaque, insulating, and spin-polarizing and show how this is related to angular mismatch, quantum mechanical interference, and out-of-plane buckling. Especially, we find that spin-polarization in the GB correlates with out-of-plane buckling. We further investigate the characteristics of these classes in simulated scanning tunnelling spectroscopy and diffusive transport along the GB which demonstrate how current can be guided along the GB.

Insights into the effect of methylammonium orientation on the crystal structural, electronic structure and optical properties of CH3NH3SnI3

Organic-inorganic hybrid halide perovskites have become an important new generation solar cell materials that are expected to significantly improve the solar conversion efficiency. In this work, the effect of methylammonium (CH3NH3) orientation on CH3NH3SnI3 perovskite is studied by using the first principles of density functional theory. We report the electronic and optical properties of methylammonium in different orientations. It is shown that CH3NH3 orientation leads to an increase in the absorption coefficient and complex refractive index of the material, a redshift in the absorption spectrum, and an enhanced absorption in the visible and near-infrared regions. We find that these changes are strongly influenced by organic-inorganic interactions and octahedral distortions. It suggests that the band gap and optical properties may be effectively modulated by the CH3NH3 rotation orientation, providing valuable insights into the behavior of CH3NH3 embedded in the inorganic octahedra of experiments.

Robustness of magnetocrystalline anisotropy and coercivity in Fe–Co–B

As a potential candidate for critical chemical element free permanent magnet, (Fe0.7Co0.3)2B, shows promising intrinsic magnetic properties, including large magnetization, high Curie temperature and moderate magnetocrystalline anisotropy (MCA). Still, the coercivity that has been achieved is relatively low. To understand and improve coercivity, we study the robustness of MCA related to the fluctuation of chemical composition and the structural distortion and its effect on coercivity in (Fe0.7Co0.3)2B from first principles DFT (density functional theory) calculation and micromagnetic simulation. A fluctuation of cobalt content of 10%, or 1% isotropic lattice strain, or 2% tetragonal distortion reduces MCA energy up to 30%. By considering randomly distributed local MCA energy reduction up to 30%, the calculated coercivity of anisotropic bulk magnets reduced from 3.6 kOe to 2.2 kOe. Rational microstructure design, such as grain size refinement and development of strong crystal texture of MCA easy-axis (i.e., degree of alignment for (Fe0.7Co0.3)2B grains), can enhance coercivity and mitigate the effect of local MCA reduction. In addition to acceptable intrinsic magnetic properties, the promising hard magnetic phase needs good MCA robustness to facilitate the development of practical magnets.

Exploring half-metallicity and pressure-induced effect in inverse heusler alloys: First principle DFT investigations of Cr2XZ (X = Ni, Pd, Pt; Z = Al, Ga, Si, Ge)

In this study, we have predicted a set of inverse Heusler alloys (HA) based on transition metals, specifically Cr2XZ (X = Ni, Pd, and Pt; Z = Al, Ga, Si, and Ge), using density functional theory (DFT) calculations. The structural, electronic, magnetic, and elastic properties, of Cr2XZ HAs have been investigated in detail to evaluate their potential for spintronic applications. Our electronic structure analysis involved the examination of band structure (BS) and density of states (DOS) to elucidate the half-metallic and magnetic characteristics of the alloys. The results indicate that Cr2XZ alloys stabilize in the F 4‾ 3 m space group in the Hg2CuTi type inverse structure, displaying a ferrimagnetic (FiM) ground state. Notably, among the inverse HAs, Cr2NiAl, and Cr2PtSi exhibit intriguing half-metallic properties with 100% spin polarization at the Fermi level (EF). Furthermore, under the influence of pressure, there is evidence of a nearly half-metallic nature in Cr2PtAl and Cr2PdGe, while the nearly half-metallic traits persist up to compressive pressures of 55 GPa and 40 GPa for Cr2PtAl, and Cr2PdGe, respectively. The Born stability criteria confirm the mechanical stability of the Cr2XZ HAs, with Cr2NiZ (Z = Al, and Ga), Cr2PdZ (Z = Ga, and Ge), and Cr2PtAl exhibiting a brittle nature, and Cr2NiZ (Z = Si, and Ge), Cr2PdZ (Z = Al, and Si), and Cr2PtZ (Z = Ga, Si, and Ge) exhibiting ductility.

EFFECT OF Sc ON THE HYDROGEN-STORAGE PERFORMANCE OF Mg2Ni: A FIRST-PRINCIPLES STUDY

The effect of metal scandium (Sc) on the hydrogen-storage properties of the magnesium-nickel (Mg2Ni) alloy has been explored using the ultrasoft pseudopotential approach, rooted in the principles of Density Functional Theory (DFT). The binding energy, lattice constant, enthalpy of formation, standard enthalpy of reaction, charge density, density of states and bond order for the Mg2-xScxNi (x = 0, 0.25, 0.5, 1) alloys and their hydrides were calculated. Furthermore, the analysis of the atomic bonding and the structural stability of Mg2-xScxNi and hydrides were also facilitated. The results show that the preference site of the Sc atom in Mg2-xScxNi (x = 0, 0.25, 0.5, 1) alloys is Mg (6i) under the condition of a Sc doping concentration of 0.25. This causes a decrease in the stability of the Mg1.75Sc0.25Ni alloy. Moreover, the addition of Sc to Mg2-xScxNiH4 weakens the interaction of H-Ni and H-Mg, thereby facilitating the hydrogen-release reaction and effectively enhancing the hydrogen-release capability of Mg2-xScxNiH4.

Quantum spin Hall effect and emergence of conducting edge states in silicene supported by MX (M=Ga, In; X=S, Se, Te) monolayer

The electronic structure of silicene supported by monolayer of different monochalcogenide MX (GaS, GaSe, GaTe and InSe) substrates has been investigated by first principle density functional theory. By calculating the formation energies and phonons, it has been seen that silicene supported by monolayer of MX remains stable. The systems retain their almost [Formula: see text] planner configurations with small buckling as that of the free standing silicene and also the Bader charge analysis shows that silicene hardly interacts with any of the MX substrates. The Dirac cone with a small gap ([Formula: see text] [Formula: see text]meV) has been observed in each of the cases. All the systems show quantum spin Hall effect and the quantum spin Hall conductivities have been estimated to be within the range [Formula: see text]S/cm, which are larger than that of the free standing silicene. Our calculations show that even if the systems have bulk band gaps but the edge states are conducting in nature.

Segregation of Al and its effect on coercivity in Nd-Fe-B

Doping a small amount of Al can effectively enhance coercivity in Nd-Fe-B magnets. We investigated the partitioning behavior of Al and its effect on coercivity in Nd-Fe-B using first principles DFT (density functional theory) calculation and micromagnetic simulation. The calculated substitution energies of Fe by Al are negative at the crystallographic sites of 4c and 8j2 while they are positive values at the other sites in Nd2Fe14B (2:14:1), implying a small solubility of Al in 2:14:1. Further, Al prefers to segregate at grain boundary (GB) and stabilize the Nd-Fe-Al phase with a Nd6Fe13Si-type tetragonal structure (6:13:1). The formation of the antiferromagnetic or weak ferrimagnetic 6:13:1-like phase depletes Fe and reduces the amount of ferromagnetic Nd–Fe type grain boundary phase (GBP), which weakens the inter-grain magnetic interaction. Micromagnetic simulations indicate that the 6:13:1-like GBP increases the pinning field of magnetic domain wall at GB and suppresses the nucleation of reversal magnetic domain on the grain surface of 2:14:1 during demagnetization process. The formation of Al-rich shell on 2:14:1 grain surface can further moderately increase the domain pinning field at GB and the nucleation field of 2:14:1 grain. Developing novel processing method to tailor Al segregation and promote formation of 6:13:1-like phase at GB can be a promising approach to improve coercivity in Nd-Fe-B magnet.

Self-reducing precursors for aluminium metal thin films: evaluation of stable aluminium hydrides for vapor phase aluminium deposition.

Thin films of Al as interconnect materials and those of AlN as wide bandgap semiconductor and piezoelectric material are of great interest for microelectronic applications. For the fabrication of these thin films via chemical vapor deposition (CVD) based routes, the available precursor library is rather limited, mostly comprising aluminium alkyls, chlorides, and few small amine-stabilized aluminium hydrides. Herein, we focused on rational precursor development for Al, their characterization and comparison to existing precursors comprising stabilized aluminium hydrides. We present and compare a series of potentially new and reported aluminium hydride precursors divided into three main groups with respect to their stabilization motive, and their systematic structural variation to evaluate the physicochemical properties. All compounds were comprehensively characterized by means of nuclear magnetic resonance spectroscopy (NMR), Fourier-transform infrared spectroscopy (FTIR), elemental analysis (EA), electron-impact ionization mass spectrometry (EI-MS) and thermogravimetric analysis (TGA). Promising representatives were further evaluated as potential single source precursors for aluminium metal formation in proof-of-concept experiments. Structure and reaction enthalpies with NH3 or H2 as co-reactants were calculated via first principles density functional theory simulations and show the great potential as atomic layer deposition (ALD) precursors for Al and AlN thin films.

Electronic phase transition, vibrational properties and structural stability of single and two polyyne chains under external electric field

Search for one dimensional (1D) van der Waals materials has become an urgent need to meet the demand as building blocks for high performance, miniaturized, lightweight device applications. Polyyne, a 1D atomic chain of carbon is the thinnest and strongest allotrope of carbon, showing promising applications in new generation low dimensional devices due to the presence of a band gap. A system of two carbon chains held together by van der Waals interaction has been theoretically postulated and shows band gap tunability under structural changes which finds applications in the realms of resistive switching and spintronics. In this study, we use first principles Density Functional Theory (DFT) to show a sharp semiconductor to metal transition along with the emergence of an asymmetry in the spin polarized density of states for single and two polyyne chains under a transverse electric field. The thermodynamic stability of the system has been substantiated through the utilization of Ab Initio Molecular Dynamics (AIMD) simulations, phonon dispersion curve analyses, and formation energy calculations. Furthermore, in addition to its dynamic stability assessment, phonon calculations have served to identify Raman-active vibrational modes which offers an invaluable non-destructive experimental avenue for discerning electronic phase transitions in response to an applied electric field. Our study presents a predictive framework for the prospective utilization of one and two polyyne chains in forthcoming flexible nano-electronic and spintronic devices. The future prospects of the system are contingent upon advancements in nano-electronics fabrication techniques and the precise construction of circuitry for harnessing spin-related applications.

First Principles Modelling of Growth of Hybrid Organic-Inorganic Films

Hybrid organic-inorganic materials fabricated with molecular layer deposition (MLD) are a special class of materials that are attracting great interest in many economically and socially relevant technological applications due to their diphasic and tunable organic-inorganic structure. Despite the growing interest in these hybrid materials, knowledge around relevant precursor chemistries and reaction mechanisms, as well as details of many determined experimental results are unknown. Density functional theory (DFT) has proven to be a powerful tool to investigate and understand the atomic level details of the precursor chemistry and address aspects of the MLD experiments.In our work, we use first principles DFT calculations to examine key steps in the mechanism of hybrid film deposition through MLD by modelling precursor-surface and precursor-precursor reactions. We explore the growth mechanism of aluminium and titanium containing hybrid films, namely alucones and titanicones. Both materials are of high interest for passivation layers in batteries. For alucones we investigate in detail the chemistry of the MLD process between the post-trimethylaluminium (TMA) pulse methyl-terminated Al2O3 surface with aromatic compounds with hydroxy and/or amino groups as reactive groups: hydroquinone (HQ), 4-aminophenol (AP) and p-phenylenediamine (PD). Double reactions of HQ, AP and PDA with the Al2O3 surface are explored in detail to assist the interpretation of the experimental findings regarding the differences found for hybrid films grown with aromatic and aliphatic organic precursors. DFT calculations show that in contrast to aliphatic organics, an upright configuration will be present for HQ, AP and PD so that the molecules are self-assembled in an upright configuration, which leads to thicker hybrid films. We predict that aromatic molecules are the best choice for stable hybrid films and their chemistry can be manipulated without degrading stability. [1]We also investigate in detail the chemistry between the most common titanium precursors, namely titanium tetrachloride (TiCl4) and tetrakis(dimethylamido)titanium (Ti(DMA)4), and ethylene glycol (EG) and glycerol (GL) as the organic precursors for the fabrication of titanicone films. We analyse the impact of the substrate on the initial MLD reactions in titanicone film growth using three different surface models: anatase TiO2, rutile TiO2 and Al2O3. This work highlights the role of the phase of TiO2 and Ti-containing precursors in production of titanicone films and provides motivation to develop a new rutile TiO2 based hybrid film suggesting that the desired film growth, flexibility and stability can be achieved. [2][1] A. Muriqi, M. Karppinen and M. Nolan, Role of terminal groups in aromatic molecules on the growth of Al2O3-based hybrid materials, Dalton Transactions, 2021, 50, 17583-17593. doi.org/10.1039/D1DT03195C.[2] Arbresha Muriqi and Michael Nolan, “Role of Titanium and Organic Precursors in Molecular Layer Deposition of “Titanicone” Hybrid Materials”, Beilstein Journal of Nanotechnology, 2022, 13, 1240–1255. doi.org/10.3762/bjnano.13.103.

Hydrogen bond reorientations driven phase transitions leading to dielectric anomaly in bis(glycinium)oxalate at high pressure and low temperature

Glycine complexes are of immense importance to fundamental science and technological applications. Bis(glycinium)oxalate is stabilized by an unusually strong hydrogen bond at ambient conditions in a centrosymmetric crystal structure. Here, using high pressure and low temperature infrared spectroscopic studies, supported by first principles density functional theory calculations, we present the mechanism of phase transformation in dense Bis(glycinium)oxalate, both at a pressure of 1.7 GPa and at temperatures below 50 K. The transition is governed by reorientations in strong hydrogen bonding network mediated by displacements in carboxylate ions, which modifies glycine conformation driving the loss of inversion symmetry. Further, we have carried out dielectric measurements, which show that the phase transformation is accompanied with a dielectric transition in the non-centrosymmetric phase of the crystal, making it a potential candidate to search for a new ferroelectric material in glycine family.