LIGA Research Articles

Ternary nitrides for hydrogen storage: Li–B–N, Li–Al–N and Li–Ga–N systems

This paper reports an investigation of hydrogen storage performance of ternary nitrides based on lithium and the Group 13 elements boron, aluminum and gallium. These were prepared by ball milling Li3N together with the appropriate Group 13 nitride—BN, AlN or GaN. Powder X-ray diffraction of the products revealed that the ternary nitrides obtained are not the known Li3BN2, Li3AlN2 and Li3GaN2 phases. At 260 °C and 30 bar hydrogen pressure, the Li–Al–N ternary system initially absorbed 3.7 wt.% hydrogen, although this is not fully reversible. We observed, for the first time, hydrogen uptake by a pristine ternary nitride of Li and Al synthesized from the binary nitrides of the metals. While the Li–Ga–N ternary system also stored a significant amount of hydrogen, the storage capacity for the Li–B–N system was near zero. The hydrogenation reaction is believed to be similar to that of Li3N, and the enthalpies of hydrogen absorption for Li–Al–N and Li–Ga–N provide evidence that AlN and GaN, as well as the ball milling process, play a significant role in altering the thermodynamics of Li3N.

The charge transfer and ion formation in liquid Li–Tl alloys

The 7Li NMR Knight shift, K, and the spin-lattice relaxation time, T1, were measured for liquid Li–Tl alloys. The K decreases rapidly with the addition of Tl up to 20at.% Tl. In the concentration from 20 to 50at.% Tl, the K decreases only slightly and the K of 50at.% Tl is 60% of K for the pure liquid Li. Such a decrease of K is considered as an indication for the strong charge transfer from Li to Tl. These tendencies are similar to those from previous studies for liquid Li–Ga and Li–In alloys. However, beyond 50at.% Tl, the K increases and reaches to an almost constant value (70% of K for the pure liquid Li). Such a back donation of charge is absent for liquid Li–Ga and Li–In alloys. It is considered that the tendency of the formation of ionic structural unit for liquid Li–Tl alloys is slightly weaker compared with the cases of liquid Li–Ga and Li–In alloys. The T1 is also discussed with the relation to the Knight shift and the electronic properties.

Bulk GaN single crystals: a reinvestigation of growth mechanism using Li3N flux

The GaN growth mechanism using Li3N flux was reinvestigated by designing a new experiment that allowed us to grow GaN simultaneously under varying Ga/Li3N molar ratios. The results confirm the two-step reactions involved in the Ga–Li3N system: Li3N+Ga→Li3GaN2+Li (1) and Li3GaN2+Ga→GaN+Li (2). It is found that reaction (2) is the main cause leading to small GaN crystals in the products. Larger GaN crystals, however, can grow by a different pathway. The growing process is concerned with the formation of Li–Ga–N melt by dissolving Li3GaN2 in Li–Ga melt after reaction (1). GaN crystals up to 3 mm grow from the Li–Ga–N melt upon cooling on the GaN particles by reaction (2). Our results suggest that it is necessary to restrain reaction (2) by choosing proper Ga/Li3N molar ratios so as to obtain GaN crystals in larger size.

Frustrated states of the spin-glass type in diluted ferrimagnetic oxides

The results of comprehensive experimental research on two model frustrated systems of dilute ferrimagnetic oxides—the slightly anisotropic cubic spinels Li0.5Fe2.5−xGaxO4 and the highly anisotropic hexagonal BaFe12−xGaxO19—are reviewed and summarized. The concentration x-T phase diagrams constructed for this class of magnets for the first time are discussed, the mechanisms of formation of disordered states of the spin-glass type (with the role of the exchange interaction and anisotropy taken into account) are examined, and the structure of the states and the influence of spatial inhomogeneity of the cluster type are considered. It is shown for the example of the Li–Ga spinels that in this class of anisotropic Heisenberg magnets with short-range exchange the form of the x-T diagram differs from the canonical form for spin-glass systems: in the reentrant region (0.9⩽x⩽1.5) one observes a new cooperative frustrated state and a line of first-order phase transitions T1(x) terminating in a critical point at x=0.8.

Growth of bulk GaN single crystals by flux method

The progresses on the growth of bulk GaN crystals by the flux method in our research group are reported in this review.The research work is mainly focused on the ternary system Li–Ga–N. The phase relations are constructed by the calculation of phase diagram (CALPHAD) technique based on the optimized thermodynamic data of the corresponding binary systems Li–N, Li–Ga and Ga–N. There exists a two-phase region of liquid+GaN at above 750 °C. The well-crystallized, transparent GaN plate-like crystals up to a size of 4 mm can be grown from the Li–Ga–N system under pressures of 1–2 N2 atmospheres. The yield and quality of the GaN crystals depend on the composition of the starting materials, the growth temperature, the cooling rate, and the position of Li3N in the crucible. Efforts are still needed to further enlarge the size of crystals.

Assessment of Li–Ga–N ternary system and GaN single crystal growth

Phase diagram of the system Li–Ga–N was constructed and assessed by using the calculation of the phase diagram (CALPHAD) method. The phase diagram suggests that GaN crystal can be grown from the Ga-rich Li–Ga–N ternary solution under 1–2 atmospheric pressure of N 2 and moderate temperature. Using starting materials Li 3N and Ga with molar ratio 1:3, colorless transparent GaN platelets with sizes 3–4 mm were obtained at 800°C and under 1 atm nitrogen atmosphere.

Preparation and characterizations of bulk GaN crystals

The growth conditions and mechanism of hexagonal GaN platelet crystals by Li flux were studied. The experimental results confirmed that these crystals crystallized from Li–Ga–N liquid phase. Photoluminescence (PL) spectra and Raman scattering spectrum of the crystals were obtained, which show that GaN crystals obtained by this method possess good crystalline quality.

Effect of Electrolyte Composition on Ni-Fe Deposition in LIGA Process

The effect of electrolyte's surface tension on Ni-Fe codeposition for MEMS application was studied. A nickel-iron microstructure was obtained inside high-aspect-ratio(210μm deep with 7μm width) microchannel. The internal stress and surface defect of the alloy microstructure are influenced by the presence of surfactant and applied current. Uniform distribution of deposit inside microstructure can be achieved by choosing proper current, surfactant and optimal control of hydrogen evolution reaction which can induce agitation and mitigate pH variation during electrodeposition.

Formation and thermal decomposition of gallium oxynitride compounds

The formation of a previously unknown crystalline phase was observed in the system Li–Ga–N–O. During the reactions of Ga2O3 with Li3N and of LiGaO2 with Li3N, a new compound with the stoichiometry Li4GaNO2 was formed. The stages in thermal decomposition of the new phase were determined.

Predictions of ground states of LiGa and NaGa

The ground and very low-lying excited states of LiGa and NaGa have been studied using high level ab initio techniques. At the QCISD(T)/6-311 + G(2df) level of theory, the 1Σ + state was found to be the most stable for both molecules. The equilibrium bond lengths and dissociation energies were found to be: R( LiGa) = 2.865 A ̊ and D 0(LiGa) = 22.3 kcal/mol and R( NaGa) = 3.174 A ̊ and D 0(NaGa) = 17.1 kcal/mol. Trends within the ground electronic states of LiB, NaB, LiAl, NaAl, LiGa and NaGa are discussed and predictions for related AlkM (Alk LiCs and MBTl) species are made.

Combination of LIGA with other microstructure technologies

Combination of LIGA with other microstructure technologies

微細加工技術と表面処理 マイクロマシンとＬＩＧＡ

微細加工技術と表面処理 マイクロマシンとＬＩＧＡ

The resistivities of liquid KGa alloys

Electrical resistivities of liquid KGa alloys were measured as a function of temperature and composition by a d.c. four-probe method. The electrical resistivity exhibits a sharp maximum value of 595 μΩ cm at 943 K and for a Ga concentration of 45 at. %. This maximum is much higher than those in LiGa and NaGa. The appearance of the maximum is discussed in terms of charge-transfer-induced anion clustering. More particularly, the possibility of local ordering resembling that of the B 2 or B 32 crystal structures is considered.

Polyanionic clustering in crystalline and liquid alkali-group-III metal alloys

A theoretical investigation of the structural and electronic properties of crystalline and liquid alloys of alkali metals with group-III metals is presented. The results suggest the validity of a generalized Zintl principle assuming at least formally complete electron transfer, so that the local coordination and the electronic DOS in, e.g., LiGa alloys becomes Ge-, As-, and finally Se-like with increasing Li-concentration and hence an increasing number of electrons per Ga atom.

Growth and characterization of large single crystals of LiGa Zintl intermetallic compound

Single crystals of the beta-LiGa Zintl intermetallic compound were grown under carefully observed conditions of chemical purity. The three crystals separated from the specially designed boron nitride crucible are believed to be parts of one single crystalline domain with 5.5 cm length and 1.3 cm diameter. Phase identification was done by X-ray diffraction. The easy cleavage plane was the (111) plane. The lattice parameter was found to be 6.17 Å, corresponding to a composition Li 0.45Ga 0.55 for the final product. The crystals are being used for studies of the electronic structure of valence and conduction bands of the material by angle resolved photoemission and inverse photoemission techniques.

The structure of LiGa

Des mesures de diffraction de neutrons pour deux echantillons du systeme Li-Ga (Li 0,5 Ga 0,5 et Li 0,77 Ga 0,23 ) indiquent une forte mise en ordre dans le liquide induite par transfert electronique des atomes de Li aux atomes de Ga

The lithium–indium system

A re-examination of the Li–In system, based on thermal and X-ray diffraction analysis of 42 alloys, shows it to be more complex than originally reported. This complexity is more consistent with the analogous Li–Tl and Li–Ga systems. The solid solubility of Li in In is about 1.5 at% Li, while that of In in Li appears to be very low. The homogeneous Li–In phase extends from about 46 at% to between 55 and 63 at% Li, depending on the temperature. Of the 11 new phases, 5 with the nominal compositions Li7In4, Li2In, Li8In3, Li3In, and Li4In(λ) are stable at room temperature, while Li5In2, Li73In27(η), Li11In4, Li4In(κ), Li6In and Li12In occur at higher temperatures.