Crystal structure and hydrogen storage property of Nd2Ni7 superlattice alloy

This study investigates the crystal structure and Pressure–composition (P–C) isotherm of Nd₂Ni₇ prepared by annealing an arc-melted ingot at 1448 K for 10 h followed by ice-water quenching. The crystal structure was further refined by X-ray Rietveld analysis based on the Ce₂Ni₇-type structure. The lattice parameters were determined as a = 0.5001(1) nm and c = 2.4437(4) nm. A single plateau was observed during the first absorption–desorption cycle. In the first absorption cycle, the maximum hydrogen capacity reached 1.22 H/M (1.58 mass%) at 233 K. The absorption and desorption plateau pressures were approximately 1.0 and 0.002 MPa, respectively. In the first desorption process, 0.63 H/M of hydrogen remained in the sample. Further, a single sloping plateau was observed in the second absorption–desorption process. Heavy peak broadening was observed in the X-ray diffraction (XRD) profile after hydrogenation, with no detection of an amorphous phase.     

Crystal structure of GdNi3 with superlattice alloy and its hydrogen absorption–desorption property

We synthesized the intermetallic compound GdNi₃, which has a PuNi₃-type structure (space group R-3m), and investigated its P–C isotherm. The refined lattice parameters were a = 0.4993(1) nm and c = 2.4536(4) nm. In the first absorption process, two plateaus were observed, and the maximum hydrogen capacity reached 1.07 H/M. In the first desorption process, a narrow and sloping plateau was observed at approximately 0.02 MPa. After the first full desorption, 0.6 H/M of hydrogen remained in the sample. This sample showed severe peak broadening in the XRD pattern, indicating that the metal sublattice deformed from the original alloy. No plateau region was observed in the second absorption–desorption cycle.     

Crystallographic hydride phase analysis and hydrogenation properties of Gd2Co7 with Ce2Ni7- and Er2Co7-type structures

We synthesized an intermetallic compound Gd₂Co₇ with Ce₂Ni₇- and the Er₂Co₇-type structures. Gd₂Co₇ with a Ce₂Ni₇-type structure was stable at 1523 K. The refined lattice parameters were a = 0.5026(1) nm and c = 2.4266(6) nm. The pressure-composition (P–C) isotherm of Ce₂Ni₇-type Gd₂Co₇ indicated that reversible hydrogen capacity reached 0.61 H/M (0.76 mass%), and two plateaus were observed in the absorption-desorption process. The crystal structures of both Gd₂Co₇H_2.5 and Gd₂Co₇H_5.5 were determined to be Ce₂Ni₇-type by X-ray diffraction.Gd₂Co₇ with Er₂Co₇-type structure is stable at temperatures below 1473 K. The refined lattice parameters were a = 0.5029(1) nm and c = 3.6403(9) nm. The determined crystal structure of Gd₂Co₇H_2.3 and Gd₂Co₇H_5.4 was Er₂Co₇-type. The P–C isotherm of Er₂Co₇-type Gd₂Co₇ was similar to that of Ce₂Ni₇-type Gd₂Co₇. In this study, the P–C isotherms of a polymorphic binary alloy with Ce₂Ni₇-type and Er₂Co₇-type structures were obtained for the first time.     

Effect of Ni content on the hydrogen storage behavior of ZrCo1−xNix alloys

ZrCo_1−xNi_x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared and their hydrogen storage behavior were studied. ZrCo_1−xNi_x alloys of compositions with x = 0, 0.1, 0.2 and 0.3 prepared by arc-melting method and characterized by X-ray diffraction analysis. XRD analysis showed that the alloys of composition with x = 0, 0.1, 0.2 and 0.3 forms cubic phase similar to ZrCo with traces of ZrCo₂ phase. A trace amount of an additional phase similar to ZrNi was found for the alloy with composition x = 0.3. Hydrogen desorption pressure–composition–temperature (PCT) measurements were carried out using Sievert's type volumetric apparatus and the hydrogen desorption pressure–composition isotherms (PCIs) were generated for all the alloys in the temperature range of 523–603 K. A single sloping plateau was observed for each isotherm and the plateau pressure was found to increase with increasing Ni content in ZrCo_1−xNi_x alloys at the same experimental temperature. A van't Hoff plot was constructed using plateau pressure data of each pressure–composition isotherm and the thermodynamic parameters were calculated for desorption of hydrogen in the ZrCo_1−xNi_x–H₂ systems. The enthalpy and entropy change for desorption of hydrogen were calculated. In addition, the hydrogen absorption–desorption cyclic life studies were performed on ZrCo_1−xNi_x alloys at 583 K up to 50 cycles. It was observed that with increasing Ni content the durability against disproportionation of alloys increases.     

Microstructure and electrochemical investigations of La0.76−xCexMg0.24Ni3.15Co0.245Al0.105 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys

The effects of substitution of Ce for La on the microstructure and electrochemical performance of La_0.76−xCe_xMg_0.24Ni_3.15Co_0.245Al_0.105 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses showed that the main phases of the alloys consist of (La, Mg)Ni₃ phase (PuNi₃-type rhombohedral structure), LaNi₅ phase (CaCu₅-type hexagonal structure) and (La, Mg)₂Ni₇ phase (Ce₂Ni₇-type hexagonal structure). The cell volume of the (La, Mg)Ni₃ phase, (La, Mg)₂Ni₇ phase and LaNi₅ phase decreased monotonously with increasing Ce content. Electrochemical investigations showed a decrease in the discharge capacity, while high rate dischargeability (HRD) first increased and then decreased with increasing Ce content. The Ce substitution for La slightly enhanced the cyclic stability of the alloy electrodes. The pressure–composition (P–C) isotherms showed that the plateau region was broadened with Ce content increased in the alloys, meanwhile, two plateaus appeared and pressure of the hydrogen absorption and desorption increased accordingly.     

Effect of Sm substitution for Gd on the electrical conductivity of fluorite-type Gd2Zr2O7

Gd_2−xSm_xZr₂O₇ (x = 0, 0.2, 0.6, 1.0, 1.4, 1.8, 2.0) ceramic powders synthesized with the chemical-coprecipitation and calcination method were pressureless-sintered at 1873 K for 10 h in air. The electrical conductivity of Gd_2−xSm_xZr₂O₇ ceramics was investigated by complex impedance spectroscopy over a frequency range of 0.01 Hz to 15 MHz. Gd_2−xSm_xZr₂O₇ is an oxide-ion conductor in the oxygen partial pressure range from 1.0 × 10⁻¹⁵ to 1.0 atm and in the temperature range of 623–873 K. The measured electrical conductivity obeys the Arrhenius relation. The activation energy and pre-exponential factor for grain-interior conductivity gradually decrease with increasing Sm content. The grain-interior conductivity varies with the Sm substitution for Gd, and reaches the maximum at the equal molar of Sm³⁺ and Gd³⁺ in Gd_2−xSm_xZr₂O₇ ceramics. A significant increase in the grain-interior conductivity is obtained by isovalent rare-earth element like Sm substitution for Gd in the temperature range of 623–873 K.     

Effect of Mg substitution on crystalline structure and hydrogenation of Gd4MgNi19

The effect of Mg substitution on Gd₄MgNi₁₉ was investigated using X-ray diffraction (XRD) and pressure-composition (P-C) isotherm measurements. Gd₄MgNi₁₉ consists of 56% Gd₂Co₇-type, 27% Ce₅Co₁₉-type, and 17% CaCu₅-type structures, which are retained in the hydride phase. Peak broadening was observed in the XRD profile of the hydride phase, while the degree of peak broadening decreased in the hydrogen-desorbed alloy after the P-C isotherm measurement. The reversible hydrogen capacity reached 1.0 H/M. There was a wide plateau region between 0.10 H/M and 0.80 H/M during the absorption-desorption process.Gd₅Ni₁₉ consists of 89% Sm₅Co₁₉-type and 11% CaCu₅-type structures. After the P-C isotherm measurement, the hydrogen-desorbed Gd₅Ni₁₉ alloy showed severe ?peak broadening in the XRD profile. The reversible hydrogen capacity was 0.80 H/M, and there was a sloping plateau in the P-C isotherm.Mg substitution decreases the severe peak broadening and lattice strain after the P-C isotherm measurement, and enhances the hydrogenation property.     

Preparation and electrochemical properties of strontium doped Pr2NiO4 cathode materials for intermediate-temperature solid oxide fuel cells

Pr_2−xSr_xNiO₄ (PSNO, x = 0.3, 0.5 and 0.8) cathode materials for intermediate-temperature solid oxide fuel cell (IT-SOFC) were synthesized by a glycine-nitrate process using Pr₆O₁₁, Ni(NO₃)₂·6H₂O and SrCO₃ powders as raw materials. Phase structure of the synthesized powders was characterized by X-ray diffraction analysis (XRD). Microstructure of the sintered PSNO samples was observed and thermal expansion coefficient (TEC) and electrical conductivity were investigated. Electrochemical impedance spectroscopy (EIS) measurement of the PSNO materials on Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte was carried out, and single cells based on the PSNO cathodes were also assembled and their performances were tested. The results show that the synthesized PSNO powders have pure K₂NiF₄-type structure and the PSNO materials are chemically stable with Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte. The sintered PSNO samples have porous and fine microstructure with pore size smaller than 1 μm. Average thermal expansion coefficient of the PSNO materials is about 12–13 × 10⁻⁶ K⁻¹ at 200–800 °C and the electrical conductivity is in the range of 70–120 Scm⁻¹ at 800 °C. Area specific resistance (ASR) of the Pr_2−xSr_xNiO₄ materials on SCO electrolyte is 0.407 Ωcm², 0.126 Ωcm² and 0.112 Ωcm² for x = 0.3, 0.5 and 0.8 at 800 °C, respectively. Maximum open circuit voltage (OCV) and power density of the single NiO-SCO/SCO/PSNO cells are 0.75 V and 298 mWcm⁻² at 700 °C, respectively, which indicates that Pr_2−xSr_xNiO₄ may be a potential cathode material for IT-SOFC.     

Preparation and characterization of Ce1−x(Gd0.5Pr0.5)xO2 electrolyte for IT-SOFCs

The Ce_1−x(Gd_0.5Pr_0.5)_xO₂ (x = 0–0.24) compositions were synthesized through the sol–gel process followed by low temperature combustion. X-ray diffraction data analysis showed that all the samples exhibit a cubic structure with single phase. The lattice parameter was calculated by rietveld refinement of XRD patterns. Dense ceramics were prepared by sintering the pellets at 1300 °C. The relative density of the samples was over 98%. The surface morphology was studied by Scanning electron microscopy (SEM). Chemical composition was analyzed by Energy dispersive spectroscopy (EDX). A.C. impedance spectroscopy measurements were carried out to study the grain, grain boundary and total ionic conductivity of co-doped ceria samples in the temperature range 150–700 °C. The Ce_0.84(Gd_0.5Pr_0.5)_0.16O₂ composition showed highest grain ionic conductivity i.e., 1.059 × 10⁻² S/cm at 500 °C which is 11.5% higher than the Ce_0.9Gd_0.1O₂ (with an activation energy 0.62 eV). At intermediate temperatures, the Ce_1−x(Gd_0.5Pr_0.5)_xO₂ materials were found to be ionic in nature.     

Phase transition and hydrogenation properties of Ce2Ni7-type Pr2Co7 during the hydrogen absorption process

The crystal structure and hydrogenation properties of Pr₂Co₇ with a Ce₂Ni₇-type structure were investigated by X-ray diffraction (XRD) and observation of the pressure–composition (PC) isotherms. The reversible hydrogen capacity reached 0.8 H/M, and two plateaus were observed in the absorption–desorption process. The two observed hydride phases, Pr₂Co₇H_2.7 and Pr₂Co₇H_7.2, were determined to have hexagonal (space group: P6₃/mmc) and orthorhombic (space group: Pbcn) crystal structures, respectively. The crystal structure transformed in the order of hexagonal with a Ce₂Ni₇-type structure (original alloy) → same Ce₂Ni₇-type structure (Pr₂Co₇H_2.7) → orthorhombic (Pr₂Co₇H_7.2). The crystal lattice of the Pr₂Co₇H_2.7 underwent anisotropic expansion along the c-axis of the original alloy, whereas that of Pr₂Co₇H_7.2 exhibited isotropic expansion. The full width at half maximum (FWHM) values for the original alloy and hydride phases during the hydrogen absorption–desorption process were evaluated based on the XRD data. The FWHM values for the main peaks decreased as the hydrogen content increased during the absorption process, indicating that the number of lattice defects did not increase upon hydrogenation. The plateau pressures during the absorption process of the second cycle were the same as those of the first cycle, which also suggests that there were no lattice defects.     

Development of sample holder for in situ neutron measurement of hydrogen absorbing alloy

We developed a sample holder for in situ measurement of hydrogen absorbing alloy. In order to prevent the hydrogen absorption by vanadium, copper is coated with 2 μm thickness on inner surface of the vanadium holder. The effect of copper coating and the performance of the holder were evaluated by neutron diffraction and PDF profiles. The lattice parameters a and c of La₂Ni₇ with Ce₂Ni₇-type structure were refined as 0.505921(4) and 2.468608(4) nm by Rietveld analysis. The Cu-Cu correlation peak around r = 0.255 nm was not observed in the PDF profile. Thus the holder is useful for in situ measurement of hydrogen absorbing alloy. The diffraction and PDF profiles of La₂Ni₇D_x (0 < x < 10.5) were collected using a deuterium pressure of 3.7 MPa, and the changes of crystal and local structures were clearly observed.     

An investigation on electrochemical and gaseous hydrogen storage performances of as-cast La1−xPrxMgNi3.6Co0.4 (x = 0–0.4) alloys

The as-cast RE–Mg–Ni-based AB₂-type La_1−xPr_xMgNi_3.6Co_0.4 (x = 0–0.4) alloys were prepared by vacuum induction furnace with a high purity helium gas as the protective atmosphere. The phase composition and microstructure of the as-cast alloys were characterized by XRD, SEM equipped with EDS. The results indicate that the as-cast alloys consist of two phases of LaMgNi₄ and LaNi₅. The measurements of the electrochemical properties show that the discharge capacity of the alloys slightly decreases with Pr content rising. As the Pr content grows from 0 to 0.4, the maximum discharge capacity decreases from 347.0 to 310.4 mAh/g. However, the cycle stability and the high-rate dischargeability of the alloy obviously augment with the Pr content increasing. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the limiting current density (I_L) first increases then decreases whereas the exchange current density I₀ of the alloys first decreases then increases with the rising amount of Pr substitution, which indicates that the electrochemical dynamic of the alloy electrode are jointly dominated by the charge-transfer resistance and diffusion ability of hydrogen atoms. The measuring of the gaseous hydrogen storage reveals two pressure plateaus appear on each pressure–concentration–isotherm (P–C–T) curve of the as-cast alloys, which correspond to the LaMgNi₄ and LaNi₅ phases. Furthermore, we note that the pressure plateau of the P–C–T curve visibly rises with Pr content increasing.     

Crystal structure and cyclic properties of hydrogen absorption–desorption in Pr2MgNi9

We investigated the crystal structure and cyclic hydrogen absorption–desorption properties of Pr₂MgNi₉. The structural model is based on the PuNi₃-type structure; the Mg atom is assumed to substitute for the Pr site in an MgZn₂-type cell. The refined lattice parameters were determined from X-ray diffraction. A wide plateau region was observed in the P–C (pressure composition) isotherm at 298 K. The maximum hydrogen capacity reached 1.12 H/M (1.62 mass%) under a hydrogen pressure of 2.0 MPa. After 1000 hydrogen absorption–desorption cycles, the hydrogen capacity was superior to that of LaNi₅ (82%). Anisotropic lattice strain occurred in the hydriding process. The anisotropic peak-broadening vector was determined to be <001>. The calculated anisotropic lattice strains of the initial cycle and after 1000 cycles were far smaller than those of LaNi₅.     

Cobalt-free composite cathode for SOFCs: Brownmillerite-type calcium ferrite and gadolinium-doped ceria

A cobalt-free composite Ca₂Fe₂O₅ (CFO) – Ce_0.9Gd_0.1O_1.95 (GDC) is investigated as a new cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Gd_0.1Ce_0.9O_1.95 (GDC) electrolyte. The cathodes had brownmillerite structure with x wt.% Gd_0.1Ce_0.9O_1.95 (GDC) – (100−x) wt.% Ca₂Fe₂O₅ (CFO), where x = 0, 10, 20, 30 and 40. The effect of GDC incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the CFO–GDC composites is investigated. The composite cathode of 30 wt.% GDC – 70 wt.% CFO (CG30) coated on Gd_0.1Ce_0.9O_1.95 electrolyte showed the lowest area specific resistance (ASR), 0.294 Ω cm² at 700 °C and 0.122 Ω cm² at 750 °C. The TEC of the CG30 cathode was 13.1 × 10⁻⁶ °C⁻¹ up to 900 °C, which is a lower value than for CFO alone (13.8 × 10⁻⁶ °C⁻¹). Long-term thermal stability and thermal cycle testing of CG30 cathodes were performed. Stable ARS values were observed during both tests without delamination at the cathode–electrolyte interface. An electrolyte-supported single cell with a 300-μm-thick GDC electrolyte and an anode-supported single cell with ∼10-μm-thick yttria-stabilized zirconia (YSZ) with a GDC buffer layer attained maximum power densities of 395 mW cm⁻² at 750 °C and 842 mW cm⁻² at 800 °C, respectively. The unique composite composition of CG30 demonstrates enhanced electrochemical performance and good thermal stability for IT-SOFCs.     

Effect of Cr doping on the structural,electrochemical properties of Li[Li0.2Ni0.2−x/2Mn0.6−x/2Crx]O2 (x = 0, 0.02, 0.04, 0.06, 0.08) as cathode materials for lithium secondary batteries

Prospective positive-electrode (cathode) materials for a lithium secondary battery, viz., Li[Li_0.2Ni_0.2−x/2Mn_0.6−x/2Cr_x]O₂ (x = 0, 0.02, 0.04, 0.06, 0.08), were synthesized using a solid-state pyrolysis method. The structural and electrochemical properties were examined by means of X-ray diffraction, cyclic voltammetry, SEM and charge–discharge tests. The results demonstrated that the powders maintain the α-NaFeO₂-type layered structure regardless of the chromium content in the range x ≤ 0.08. The Cr doping of x = 0.04 showed improved capacity and rate capability comparing to undoped Li[Li_0.2Ni_0.2Mn_0.6]O₂. ac impedance measurement showed that Cr-doped electrode has the lower impedance value during cycling. It is considered that the higher capacity and superior rate capability of Cr-doping samples would be ascribed to the reduced resistance of the electrode during cycling.     

Electrochemical performance of La2Cu1−xCoxO4 cathode materials for intermediate-temperature SOFCs

K₂NiF₄-type structure oxides La₂Cu_1−xCo_xO₄ (x = 0.1, 0.2, 0.3) are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The materials are characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. The results show that no reaction occurs between La₂Cu_1−xCo_xO₄ electrode and Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte at 1000 °C. The electrode forms good contact with the electrolyte after sintering at 800 °C for 4 h in air. The electrode properties of La₂Cu_1−xCo_xO₄ are studied under various temperatures and oxygen partial pressures. The optimum composition of La₂Cu_0.8Co_0.2O₄ results in 0.51 Ω cm² polarization resistance (R_p) at 700 °C in air. The rate limiting step for oxygen reduction reaction (ORR) is the charge transfer process. La₂Cu_0.8Co_0.2O₄ cathode exhibits the lowest overpotential of about 50 mV at a current density of 48 mA cm⁻² at 700 °C in air.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Hydrocracking of Jatropha oil over Ni-H3PW12O40/nano-hydroxyapatite catalyst

The Ni-H₃PW₁₂O₄₀/nano-hydroxyapatite catalyst with H₃PW₁₂O₄₀ (HPW) loading was prepared by impregnation method and performed through hydrocracking of Jatropha oil in a fixed-bed reactor. The catalyst was characterized by N₂ adsorption–desorption, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia (NH₃-TPD), thermogravimetric analysis (TGA). The conversion of Jatropha oil over Ni-HPW (30 wt%)/nHA was 100%, the liquid yield of liquid product was 83.4%, the ratio of i/n-paraffins was 1.64 at 360 °C, 3 MPa, H₂/oil (v/v) = 600 and LHSV = 2 h⁻¹. The pour point of final product oil was −28 °C and the catalyst was used without sulfurization.     

Fabrication and characterization of a co-fired La0.6Sr0.4Co0.2Fe0.8O3−δ cathode-supported Ce0.9Gd0.1O1.95 thin-film for IT-SOFCs

A dense membrane of Ce_0.9Gd_0.1O_1.95 on a porous cathode based on a mixed conducting La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ was fabricated via a slurry coating/co-firing process. With the purpose of matching of shrinkage between the support cathode and the supported membrane, nano-Ce_0.9Gd_0.1O_1.95 powder with specific surface area of 30 m² g⁻¹ was synthesized by a newly devised coprecipitation to make the low-temperature sinterable electrolyte, whereas 39 m² g⁻¹ nano-Ce_0.9Gd_0.1O_1.95 prepared from citrate method was added to the cathode to favor the shrinkage for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ. Bi-layers consisting of <20 μm dense ceria film on 2 mm thick porous cathode were successfully fabricated at 1200 °C. This was followed by co-firing with NiO–Ce_0.9Gd_0.1O_1.95 at 1100 °C to form a thin, porous, and well-adherent anode. The laboratory-sized cathode-supported cell was shown to operate below 600 °C, and the maximum power density obtained was 35 mW cm⁻² at 550 °C, 60 mW cm⁻² at 600 °C.     

Cyclic stability and high rate discharge performance of (La,Mg)5Ni19 multiphase alloy

The cyclic stability and high rate discharge performance of (La,Mg)₅Ni₁₉ multiphase alloy were investigated in this work. The results show that the alloy is composed of Pr₅Co₁₉-type (2H), Ce₅Co₁₉-type (3R), CaCu₅-type and Ce₂Ni₇-type phase after annealing at 1123 K. The total phase abundance of Pr₅Co₁₉-type (2H) and Ce₅Co₁₉-type (3R) is 63.3%. That composition decides the good cyclic stability both in repeated hydriding/dehydriding and charging/discharging process for this alloy. Moreover, the alloy shows the higher high rate discharge capacity at room temperature and it remains 140 mA h/g at the current density of 3600 mA/g.