Hydride Diffusion Research Articles

Multi-dimensional morphology of hydride diffusion layer and associated sequential twinning in commercial pure titanium

The dominant hydride precipitates have been well demonstrated to follow two types of orientation relationships (ORs) with Ti matrix: OR1 with {0001}//{001}, <12¯10>//<110> and OR2 with {0001}//{11¯1}, <12¯10>//<110>. Within the grains with special orientations, the complicated interactions of different hydride variants inside Ti-hydride diffusion layer are characterized in this work. For OR1 hydride layer, the orientations of {101¯0} plane parallel to the sample surface and a-axis parallel to the normal direction prefer multiple OR1 variants. The orientations favorable for OR2 hydride layer are: {101¯3} plane parallel to sample surface corresponding to the layer with one OR2 variant dominated and c-axis parallel to the surface normal with multiple OR2 variant layer preferred. Furthermore, {101¯2} extension twins and {112¯2} contraction twins are activated to accommodate the OR2 hydride-induced surface expansion and local misfit strain. The stimulation of these two twins is also orientation-dependent: {101¯2} and {112¯2} twins are observed in the grains with c-axis parallel to and deviated from the surface normal, respectively. The further variant selection for each twin mode is performed through shear accommodation of hydride-twin pairs.

Nanoindentation study of hydride diffusion layer in commercial pure titanium

In this work, the mechanical properties of hydride diffusion layer were thoroughly researched by nanoindentation technique. For the first time, the clear section microstructure of hydride diffusion layer was revealed under scanning electron microscope with complicated interactions of hydride plates near the interface between hydride layer and titanium matrix. The hydride layer section has higher hardness and lower modulus towards titanium matrix due to the hard nature and easier crack nucleation of hydride precipitation. Besides, the hardness of titanium matrix shows considerable anisotropy. The anisotropic hardness of sample surface was studied before and after hydrogen charging. The hardness of titanium matrix decreases with the increase of deviation angle between c-axis and surface normal. The hydride layer formed in the titanium grain with more favorable orientation for hydride transformation tends to possess higher indentation hardness.

Vanadium Hydride as an Ammonia Synthesis Catalyst

AbstractEarly 3d transition metals, such as Ti, V, or Nb are known to be inactive for the Haber‐Bosch process, due to their strong M−N bonds. However, recently some hydride compounds have been found to effectively counteract this effect, imparting catalytic activity on a wide range of elements. With these hydride catalysts, hydride (and nitride) bulk diffusion mechanisms have been proposed; if so, more open structures should enhance their activity. Here, we expand the study to hydrides of other early transition metals, V and Nb. These metals benefit from body‐centered cubic (bcc) related structures which enhance hydride diffusion, in addition to having relatively lower M−N bond strengths. The activity of vanadium hydride, most likely with an active composition of VH0.44N0.16, is superior to the previously reported BaTiO2.5H0.5, and comparable to TiH2 and Cs−Ru/MgO at 400 °C under 5 MPa. These results show that there is more potential for developing new single‐phase hydride catalysts of previously overlooked elements without sacrificing activity.

Chemical Pressure-Induced Anion Order-Disorder Transition in LnHO Enabled by Hydride Size Flexibility.

While cation order-disorder transitions have been achieved in a wide range of materials and provide crucial effects in various physical and chemical properties, anion analogues are scarce. Here we have expanded the number of known lanthanide oxyhydrides, LnHO (Ln = La, Ce, Pr, Nd), to include Ln = Sm, Gd, Tb, Dy, Ho, and Er, which has allowed the observation of an anion order-disorder transition from the anion-ordered fluorite structure ( P4/ nmm) for larger Ln3+ ions (La-Nd) to a disordered arrangement ( Fm3̅ m) for smaller Ln3+ (Sm-Er). Structural analysis reveals that with the increase of Ln3+ radius (application of negative chemical pressure), the oxide anion in the disordered phase becomes too under-bonded, which drives a change to an anion-ordered structure, with smaller OLn4 and larger HLn4 tetrahedra, demonstrating that the size flexibility of hydride anions drives this transition. Such anion ordering control is crucial regarding applications that involve hydride diffusion such as catalysis and electrochemical solid devices.

On Hydride Diffusion in Transition Metal Perovskite Oxyhydrides Investigated via Deuterium Exchange

Perovskite oxyhydrides may find diverse applications, ranging from catalysis, topochemical synthesis to solid state ionics, but the understanding of their hydride transport behavior has remained limited. Here, gaseous hydrogen exchange and release experiments were analyzed using the Kissinger method to estimate the activation energy (Ea) for H/D exchange and H2 release in BaTiO3–xHx (x = 0.35–0.60) and LaSrCoO3H0.70. It is revealed that, for each BaTiO3–xHx at a given hydride concentration (x), both H/D exchange and H2 release experiments provide similar Ea values. For BaTiO3–xHx with different x, the obtained Ea values significantly decrease with increasing x until around 0.4; beyond 0.4, it becomes nearly constant (200–220 kJ mol–1). This observation suggests that the diffusion process in the low hydride concentration (x < 0.4) includes oxide as well as hydride diffusion, whereas, for 0.4 < x (<0.75), only hydride migrates, with second-nearest-neighbor (2NN) jumps as a rate-determining process, which is...

Study of Phase Stability and Hydride Diffusion Mechanism of BaTiO3 Oxyhydride from First-Principles

First-principles calculations were performed to study structural, electronic and hydride diffusion properties of BaTiO3 oxyhydride. In agreement with experiment (Nat. Mater. 2012, 11, 507 and J. Am. Chem. Soc. 2012, 134, 8782), we find that the incoming H species occupy the anion vacancy sites left by oxygen, forming the stable hydride anions H–1. As a result of the electron doping introduced by H species, both interstitial H and hydride anion H–1 can induce metallicity and eliminate ferroelectricity in BaTiO3. We further clarify the role of the migration of the interstitial H in determining the hydrogen diffusion properties of the oxyhydrides. A low diffusion barrier was predicted, responsible for high hydrogen diffusion mobility observed in experiment. Based on our results, we demonstrate that BaTiO3 oxyhydride can be used as a mixed electron/hydride conductor, displaying the promising applications as the electrolytes for solid-oxide fuel cells.

Epitaxial Thin Films of ATiO3–xHx (A = Ba, Sr, Ca) with Metallic Conductivity

Epitaxial thin films of titanium perovskite oxyhydride ATiO(3-x)H(x) (A = Ba, Sr, Ca) were prepared by CaH(2) reduction of epitaxial ATiO(3) thin films deposited on a (LaAlO(3))(0.3)(SrAl(0.5)Ta(0.5)O(3))(0.7) substrate. Secondary ion mass spectroscopy detected a substantial amount and uniform distribution of hydride within the film. SrTiO(3)/LSAT thin film hydridized at 530 °C for 1 day had hydride concentration of 4.0 × 10(21) atoms/cm(3) (i.e., SrTiO(2.75)H(0.25)). The electric resistivity of all the ATiO(3-x)H(x) films exhibited metallic (positive) temperature dependence, as opposed to negative as in BaTiO(3-x)H(x) powder, revealing that ATiO(3-x)H(x) are intrinsically metallic, with high conductivity of 10(2)-10(4) S/cm. Treatment with D(2) gas results in hydride/deuteride exchange of the films; these films should be valuable in further studies on hydride diffusion kinetics. Combined with the materials' inherent high electronic conductivity, new mixed electron/hydride ion conductors may also be possible.