Thermodynamic stability of alkali-metal–zinc double-cation borohydrides at low temperatures

Huan, Tran Doan; Amsler, Maximilian; Sabatini, Riccardo; Tuoc, Vu Ngoc; Le, Nam B.; Woods, Lilia M.; Marzari, Nicola; Goedecker, Stefan

doi:10.1103/physrevb.88.024108

Cited by 31 publications

(24 citation statements)

References 74 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For these materials, PBE calculations predict very low-density structures to be thermodynamically stable while, at the same time, produce large deviations when optimizing their complicated experimental structures. 51 By taking into account the vdW interactions via the non-local density functional vdW-DF2, 52 the optimized geometries agree better with the experimental data. It is worth noting that for the borohydrides with simple ionic crystalline structures, e.g., LiBH 4 , NaBH 4 , and KBH 4 , the calculated results with vdW-DF2 are not always better than those with PBE, 51 indicating that, presumably, the dispersion interactions play a minor role in the crystalline materials dominated by ionic and covalent bonds.…”

Section: Effects Of Exchange-correlation Functionals and Vdw Intmentioning

confidence: 84%

First-principles predicted low-energy structures of NaSc(BH4)4

Tran

Amsler

Botti

et al. 2014

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

According to previous interpretations of experimental data, sodium-scandium doublecation borohydride NaSc(BH 4 ) 4 crystallizes in the crystallographic space group Cmcm where each sodium (scandium) atom is surrounded by six scandium (sodium) atoms. A careful investigation of this phase based on ab initio calculations indicates that the structure is dynamically unstable and gives rise to an energetically and dynamically more favorable phase with C222 1 symmetry and nearly identical x-ray diffraction pattern. By additionally performing extensive structural searches with the minima-hopping method we discover a class of new low-energy structures exhibiting a novel structural motif in which each sodium (scandium) atom is surrounded by four scandium (sodium) atoms arranged at the corners of either a rectangle with nearly equal sides or a tetrahedron. These new phases are all predicted to be insulators with band gaps of 7.9 − 8.2 eV. Finally, we estimate the influence of these structures on the hydrogen-storage performance of NaSc(BH 4 ) 4 .

show abstract

Section: Effects Of Exchange-correlation Functionals and Vdw Intmentioning

confidence: 84%

First-principles predicted low-energy structures of NaSc(BH4)4

Tran

Amsler

Botti

et al. 2014

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…This method, which relies on extensively exploring the DFT energy landscape of a given chemical composition, has successfully been used for various classes of crystalline materials 34,[40][41][42] The phonon frequency spectra and related vibrational free energies for each system are examined within the supercell approach as implemented in the phonopy package. 43,44 Calculations of the transport properties, such as the electrical conductivity and Seebeck coefficient for the various structures, are carried utilizing the constant relaxation time τ approximation as implemented in the BoltzTrap code.…”

Section: Methodsmentioning

confidence: 99%

High-pressure phases ofMg2Sifrom first principles

Huan

Tuoc

et al. 2016

Phys. Rev. B

Self Cite

View full text Add to dashboard Cite

First principles calculations are presented to resolve the possible pressure-dependent phases of Mg2Si. Although previous reports show that Mg2Si is characterized by the cubic antiflurite F m3m structure at low pressures, the situation at higher P is less clear with many contradicting results. Here we utilize several methods to examine the stability, electron, phonon, and transport properties of this material as a function of pressure and temperature. We find that Mg2Si is thermodynamically stable at low and high pressures. Between 6 and 24 GPa, Mg2Si can transform into Mg9Si5, a defected compound, and vice versa, without energy cost. Perhaps this result is related to the aforementioned inconsistency in the structures reported for Mg2Si within this pressure range. Focusing solely on Mg2Si, we find a new monoclinic C2/m structure of Mg2Si, which is stable at high pressures within thermodynamical considerations. The calculated electrical conductivity and Seebeck coefficient taking into account results from the electronic structure calculations help us understand better how transport can be affected in this material by modulating pressure and temperature.

show abstract

“…Local geometry optimizations were then used to obtain the equilibrium structure. This method has been successfully applied in the past for various classes of crystalline materials, including inorganic [29][30][31] and organometallic [32] compounds.…”

mentioning

confidence: 99%

Pathways towards ferroelectricity in hafnia

et al. 2014

Self Cite

View full text Add to dashboard Cite

The question of whether one can systematically identify (previously unknown) ferroelectric phases of a given material is addressed, taking hafnia (HfO2) as an example. Low free energy phases at various pressures and temperatures are identified using a first-principles based structure search algorithm. Ferroelectric phases are then recognized by exploiting group theoretical principles for the symmetry-allowed displacive transitions between non-polar and polar phases. Two orthorhombic polar phases occurring in space groups P ca21 and P mn21 are singled out as the most viable ferroelectric phases of hafnia, as they display low free energies (relative to known non-polar phases), and substantial switchable spontaneous electric polarization. These results provide an explanation for the recently observed surprising ferroelectric behavior of hafnia, and reveal pathways for stabilizing ferroelectric phases of hafnia as well as other compounds.Commonly known structural phases of hafnia (HfO 2 ) are centrosymmetric, and thus, non-polar. Hence, recent observations of ferroelectric behavior of hafnia thin films (when doped with Si, Zr, Y, Al or Gd) [1][2][3][4][5][6][7] are rather surprising as ferroelectricity requires the presence of switchable spontaneous electrical polarization. The emergence of non-polar hafnia-as a linear high dielectric constant (or high-κ) successor to SiO 2 -for use in modern electronic devices (e.g., field-effect transistors) is now well-established [8,9]. If the origins of its unexpected ferroelectricity can be understood and appropriately harnessed, hafnia-based materials may find applications in nonvolatile memories and ferroelectric field effect transistors as well.A broader question that arises within this context, and also the one that will be addressed directly in this contribution, is whether one can systematically identify ferroelectric phases of a given material system. We show that this can indeed be accomplished and ascertained, for the example of hafnia, in two steps. First, a computationbased structure search method, e.g., the minima-hopping method [10][11][12], is used to identify low-energy phases at various pressures and temperatures. Then, ferroelectric phases are singled out by applying the group theoretical symmetry reduction principles, established by Shuvalov for ferroelectricity [13]. These principles allow for the systematic identification of all possible lower symmetry proper ferroelectric phases that can result from highersymmetry non-polar prototype (parent) phases.Using this approach, we find two ferroelectric phases of hafnia, belonging to the P ca2 1 and P mn2 1 orthorhombic space groups, which are close in free energy with the known non-polar equilibrium phases of hafnia over a wide temperature and pressure range. Figure 1(a) displays the computed equilibrium phase diagram of hafnia indicating the regimes at which the known non-polar phases are stable. This includes the low-temperature lowpressure P 2 1 /c monoclinic phase, high-pressure P bca and P nma orthorhombic p...

show abstract

Thermodynamic stability of alkali-metal–zinc double-cation borohydrides at low temperatures

Cited by 31 publications

References 74 publications

First-principles predicted low-energy structures of NaSc(BH4)4

First-principles predicted low-energy structures of NaSc(BH4)4

High-pressure phases ofMg2Sifrom first principles

Pathways towards ferroelectricity in hafnia

Contact Info

Product

Resources

About