Synthesis and performance of Y-doped La0.7Sr0.3CrO3−δ as a potential anode material for solid oxygen fuel cells

Y-doped La_0.7Sr_0.3CrO_3−δ is a promising anode catalyst for solid oxygen fuel cell (SOFC). The performances of chemical and physical are measured by SEM, XRD and FT-IR. The conductivities of catalyst are measured by DC four-probe method in 20% H₂S-N₂, 3% H₂-N₂ and air from 573 K to 1173 K, respectively. The results show that Y-doped La_0.7Sr_0.3CrO_3−δ powders have perfect perovskite phase structure with no extra peaks and exhibit good chemical compatibility with Ce_0.8Sm_0.2O_1.9 (as electrolyte) in air. Through XRD and FT-IR analysis no sulfur-containing species is detected after exposure to the 20% H₂S at 1173 K for 5 h. Meanwhile, Y-doped La_0.7Sr_0.3CrO_3−δ shows that the highest conductivity is 0.21 S/cm at 1173 K in H₂S. The open circuit voltages are 0.85 V at 1173 K in H₂S and 1.04 V at 823 K in H₂. The maximal power densities are 12.4 mW/cm² in H₂S and 1.59 W/cm² in H₂ for cells comprising Y-doped La_0.7Sr_0.3CrO_3−δ-Sm_0.2Ce_0.8O_1.9/Sm_0.2Ce_0.8O_1.9/Ag.     

Effect of nickel substitution on defect chemistry, electrical properties, and dimensional stability of calcium-doped yttrium chromite

The effect of nickel substitution on defect chemistry, electrical properties, and dimensional stability of calcium-doped yttrium chromite was studied for use as an interconnect material in high temperature solid oxide fuel cells (SOFCs). The compositions of Y_0.8Ca_0.2Cr_1 − xNi_xO_3 ± δ (x = 0-0.15), prepared using the glycine nitrate process, showed single phase orthorhombic perovskite structures over a wide range of oxygen partial pressures (4.6 × 10^− 20 atm ≤ pO₂ ≤ 0.21 atm at 900 °C). X-ray diffraction (XRD) analysis indicated that most of the nickel ions replacing chromium ions are divalent and act as acceptor dopants, leading to a substantial increase in conductivity. In particular, the conductivity at 900 °C in air increased from 10 S/cm to 34 S/cm with 15% nickel substitution, and an increase in charge carrier density was confirmed by Seebeck measurements, which validated the predominant Ni²⁺ oxidation state. A point defect model was derived, and the relationship between electrical conductivity and oxygen partial pressure was successfully fitted into the proposed model. The defect modeling results indicated that nickel substitution improves the stability of calcium-doped yttrium chromite toward reduction and suppresses the oxygen vacancy formation, which results in significantly increased electrical conductivity in reducing environment. The electrical conductivity of Y_0.8Ca_0.2Cr_0.85Ni_0.15O_3 ± δ at 900 °C in reducing atmosphere (pO₂ = 10^− 17 atm) was 5.8 S/cm, which was more than an order of magnitude higher than that of Y_0.8Ca_0.2CrO_3 ± δ (0.2 S/cm). Improved stability in reducing atmosphere was further confirmed by dilatometry measurements showing reduced isothermal “chemical” expansion, and the isothermal expansion in reducing atmosphere (pO₂ = 10^− 17 atm) at 900 °C decreased from 0.07% for Y_0.8Ca_0.2CrO_3 ± δ to 0.03% for Y_0.8Ca_0.2Cr_0.85Ni_0.15O_3 ± δ. Based on these results, enhanced electrical performance and mechanical integrity is expected with nickel substitution on calcium-doped yttrium chromite in SOFC operating conditions.     

Performance and stability of niobium-substituted Ba0.5Sr0.5Co0.8Fe0.2O3 − δ membranes

The phase stability, thermal expansion, electrical conductivity, and oxygen permeation of perovskite-type oxides Ba_0.5Sr_0.5(Co_0.8Fe_0.2)_1 − xNb_xO_3 − δ (x = 0 − 0.2) have been investigated. Room-temperature X-ray diffraction of as-prepared powders indicates that in the investigated compositional range solid solutions are formed. Long-term annealing experiments both in flowing air and nitrogen, at 750 °C, demonstrate that the phase instability observed in parent Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ (BSCF) is suppressed already at the minimum substitution of 5 mol% of niobium for (Co, Fe). Both electrical conductivity and thermal expansion are found to decrease with increasing niobium concentration, which behaviors can be explained by defect chemical considerations, taking into account charge compensation mechanisms by doping BSCF with Nb⁵⁺ donor cations. The oxygen permeation flux of 10 mol% Nb-substituted BSCF, in the range 800-900 °C, is reduced by 10% relative to that found for parent BSCF. Switching from helium to a CO₂-containing purge gas results in a severe reduction or cessation of the oxygen flux. Options are discussed to avoid undesired formation of surface carbonates.     

Thermal, electrical, and electrochemical properties of Lanthanum-doped Ba0.5Sr0.5 Co0.8Fe0.2O3-δ

Crystal structure, thermogravimetry (TG), thermal expansion coefficient (TEC), electrical conductivity and AC impedance of (Ba_0.5Sr_0.5)_1-xLa_xCo_0.8Fe_0.2O_3-δ (BSLCF; 0.05?x?0.20) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. A single cubic pervoskite was observed by X-ray diffraction (XRD). The TEC of BSLCF was increasing slightly with the increasing content of La, and all the compounds showed abnormal expansion at high temperature. Proved by the TG result, it was associated with the loss of lattice oxygen. The electrical conductivity, which is the main defect of Ba_0.5Sr_0.5 Co_0.8Fe_0.2O_3-δ (BSCF), was improved by La doping, e.g., the compound of x=0.20 demonstrated a conductivity of σ=376 S cm⁻¹ at 392 °C. The increase of electrical conductivity resulted from the increased concentration of charge carrier induced by La doping. In addition, the AC impedance revealed the better electrochemical performance of BSLCF. For example, at 500 °C, the sample with composition x=0.15 yielded the resistance values of 2.12 Ω cm², which was only 46% of BSCF.     

Stability, oxygen permeability and chemical expansion of Sr(Fe,Al)O3 − δ- and Sr(Co,Fe)O3 − δ-based membranes

Perovskite-type SrFe_0.7Al_0.3O_3 − δ and SrCo_0.8Fe_0.2O_3 − δ, and two related dual-phase composites with nominal compositions (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 and (SrCo_0.8Fe_0.2O_3 − δ)_0.7(SrAl₂O₄)_0.3, were comparatively studied employing controlled-atmosphere dilatometry, thermogravimetry, Mössbauer spectroscopy, and measurements of steady-state oxygen permeation fluxes through dense ceramic membranes. The composite materials display lower thermal and chemical expansion compared to the parent single-phase perovskites. The thermal expansion coefficients at 1023-1223 K are however still high, (20-23) × 10^− 6 K^− 1 at atmospheric oxygen pressure and (17-18) × 10^− 6 K^− 1 at p(O₂) = 10 Pa, thus limiting the range of possible membrane reactor configurations. Sr(Co,Fe)O_3 − δ-based materials exhibit extensive vacancy-ordering processes in inert atmospheres, resulting in a slow relaxation of the oxygen nonstoichiometry, chemical expansion and oxygen permeation fluxes. In comparison to Sr(Fe,Al)O_3 − δ, the stability of cobalt-containing ceramics in CO₂ is also poor, which leads to a partial blocking of the membrane surface by decomposition products and degradation of the oxygen transport. Thermogravimetric analysis showed that the interaction with carbon dioxide occurs even at elevated temperatures, up to 1223 K. Under high oxygen chemical potential gradients such as air/(H₂-H₂O), the composite membranes showed kinetically stable operation without bulk decomposition at 1073 K. The kinetic stabilization associated with surface-limited oxygen permeation was confirmed by the conversion-electron Mössbauer spectroscopy analysis of one (SrFeO_3 − δ)_0.7(SrAl₂O₄)_0.3 membrane exposed to dry CH₄ at 1173 K, where no traces of Fe²⁺ and metallic iron were detected in the reduced surface layer.     

Study of La0.8Sr0.2Co0.2Cr0.8O3 − δ as a candidate coating material for the positive current collector in Na/S battery

Perovskite La_0.8Sr_0.2Co_0.2Cr_0.8O_3 − δ (LSCC) ceramic synthesized by the conventional ceramic processing technique was studied as a novel coating material for the cathode current collector in Na/S battery. Its structure, electrical conductivity, density and thermal expansion coefficient (TEC) were investigated. The corrosion performance of LSCC was in particular evaluated by electrochemical techniques in combination with long-term dip-immersion tests. The results indicated that LSCC exhibited excellent corrosion resistance in molten sodium tetrasulfide at 350 °C. The corrosion current density i_corr (0.081 mA cm^− 2) was much lower than that of 316 L stainless steel by approximately two orders of magnitude. The corrosion rate of LSCC deduced from immersion test was as low as about 12 μm year^− 1.     

Solid solution formation, densification and ionic conductivity of Gd- and Sm-doped ceria

The processes of solid solution formation, densification and electrical conductivity in samaria and gadolinia-doped ceria solid electrolytes were studied by Raman spectroscopy, density and impedance spectroscopy measurements. Bulk specimens of Ce_0.9Gd_0.1O_1.95 and Ce_0.8Sm_0.2O_1.9 were prepared by solid state reactions at several dwell temperatures and holding times. Hydrostatic density results show a fast increase in sintered density up to 1 h holding time. Raman spectra of specimens sintered for 1 h show a prominent band at 463 cm^− 1 assigned to the cubic fluorite-type lattice of cerium oxide, and low-intensity bands at 344 and 363 cm^− 1 attributed to free samarium and gadolinium sesquioxides, respectively. Solid solution completion was achieved only at temperatures above 1400 °C. Electrical conductivity measurements were used to study mass transport. Analysis of impedance data allowed for determining the activation energy for cation diffusion in Ce_0.9Gd_0.1O_1.95 and Ce_0.8Sm_0.2O_1.9 sintered specimens.     

Sinteractivity, proton conductivity and chemical stability of BaZr0.7In0.3O3-δ for solid oxide fuel cells (SOFCs)

In³⁺ was used as dopant for BaZrO₃ proton conductor and 30 at%-doped BaZrO₃ samples (BaZr_0.7In_0.3O_3-δ, BZI) were prepared as electrolyte materials for proton-conducting solid oxide fuel cells (SOFCs). The BZI material showed a much improved sinteractivity compared with the conventional Y-doped BaZrO₃. The BZI pellets reached almost full density after sintering at 1600 °C for 10 h, whereas the Y-doped BaZrO₃ samples still remained porous under the same sintering conditions. The conductivity measurements indicated that BZI pellets showed smaller bulk but improved grain boundary proton conductivity, when compared with Y-doped BaZrO₃ samples. A total proton conductivity of 1.7 × 10⁻³ S cm⁻¹ was obtained for the BZI sample at 700 °C in wet 10% H₂ atmosphere. The BZI electrolyte material also showed adequate chemical stability against CO₂ and H₂O, which is promising for application in fuel cells.     

Improved cathode/electrolyte interface of SOFC

The electrochemical performance of porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ (LSCF) cathodes is improved by inserting a dense LSCF layer. A 200 nm thin layer is deposited on the electrolyte substrate by pulsed laser deposition, prior to the screen printing process. This procedure enhances the adherence of the porous cathode layer to the electrolyte and allows a lower sintering temperature, which reduces grain growth during sintering. In air a decrease in polarization resistance with a factor of 3 is observed for electrodes sintered at 1100 °C. The apparent electrolyte resistance is also reduced with the dense PLD layer. A remarkable change in Po₂ dependence is observed for the Gerischer parameters that describe part of the electrode impedance, indicating a possible change in the oxygen transfer mechanism.     

Oxygen relaxation and phase transition in GdBaCo2O5 + δ oxide

Electrical conductivity, internal friction techniques and dilatometer have been used to investigate the oxygen relaxation, phase transition and thermal expansion behavior of GdBaCo₂O_5 + δ. The main electronic charge carriers in GdBaCo₂O_5 + δ are electronic holes, which could be assigned to the formation of Co⁴⁺. The oxygen exchange kinetics intensely depends on oxygen partial pressure and is also closely related to temperature. Both electrical conductivity and internal friction give rise to an abnormal at about 75 °C, which are related to the insulator-metal transition occurring in GdBaCo₂O_5 + δ. One large relaxation internal friction peak, due to the motion of oxygen within Gd-O plane, is also found in the oxide. The average thermal expansion coefficient (TEC) of GdBaCo₂O_5 + δ is about 21.4 × 10⁻⁶ K⁻¹ between 500 °C and 900 °C.     

Low temperature synthesis and superconducting properties of polycrystalline T′-(La,Sm)2CuO4

La_2−xSm_xCuO_4+δ with the Nd₂CuO₄ structure was synthesized by precipitation from fused alkaline hydroxide, CsOH, at 400 °C. The as-sintered polycrystalline samples showed no diamagnetic signal, but after post-annealing in vacuum of ≈10⁻⁸ atm at 650–700 °C, the samples with x = 0.1 and 0.3 exhibited superconductivity at T_c on = 25 K. The volume fraction of the superconducting phase estimated from the slope of the Zero-Field-Cooled magnetization data was over 30% for x = 0.3, which confirmed that the La_1.7Sm_0.3CuO_4+δ is a bulk superconductor.     

Electrical properties of bulk and grain boundaries of scandia-stabilized zirconia co-doped with yttria and ceria

The electrical properties of bulk and grain boundaries of scandia-stabilized zirconia co-doped with yttria and ceria have been determined as a function of temperature (300 < T/°C < 700) and oxygen partial pressure [10^− 24 ≤ p(O₂)/bar ≤ 1, T = 700 °C] by application of impedance spectroscopy. The yttria and ceria contents of Ce_xY_0.2 − xSc_0.6Zr_3.2O_8 − δ (0 ≤ x ≤ 0.2) have been varied systematically. Homogeneous samples have been prepared by means of a sol-gel (glycine-nitrate) combustion process. The ionic conductivity in air is almost independent of composition with typical values around 0.03-0.04 S cm^− 1 for the bulk at 700 °C. A significant decrease of the ionic conductivities of bulk and grain boundaries is found for samples co-doped with ceria at low oxygen partial pressures [p(O₂) < 10^− 15 bar, T = 700 °C]. Activation energies for the ionic transport in oxidizing (air) and reducing (1%-H₂/Ar) atmospheres have been extracted from Arrhenius-plots. The oxygen nonstoichiometry in 1%-H₂/Ar has been investigated by employing thermogravimetry. The decrease of the ionic conductivity under reducing conditions is accompanied by an increase of the corresponding high temperature activation energy of the bulk, which is interpreted in terms of defect association or clustering.     

Investigations on the thermo-chemical stability and electrical conductivity of K-doped Ba3 − xKxCaNb2O9 − δ (x = 0.5, 0.75, 1, 1.25)

In this paper, we report the synthesis, crystal structure and electrical transport properties of new K-doped Ba₃CaNb₂O₉ (BCN) and investigate their chemical stability in H₂O and pure CO₂ at elevated temperature. The powder X-ray diffraction (PXRD) of Ba_2.5K_0.5CaNb₂O_9 − δ, Ba_2.25K_0.75CaNb₂O_9 − δ, Ba₂KCaNb₂O_9 − δ, and Ba_1.75K_1.25CaNb₂O_9 − δ showed the formation of a single-phase double perovskite (A₃BB^/₂O₉)-like cell with a lattice constant of a ∼ 2a_p (where a_p is a simple perovskite cell of ∼ 4 Å). Perovskite-like structure was found to be retained after treating with CO₂ at 700 °C and also after boiling H₂O for 120 h. The lattice constant of CO₂ and H₂O treated samples was found to be comparable to that of the corresponding as-prepared compound. The total electrical conductivity of all the investigated K-doped BCN increases with increasing K content in BCN in various atmospheres, including air, dry H₂, wet N₂ and wet H₂. The electrical conductivity in dry and wet H₂ atmospheres was found to be higher than that of air in the temperature range of 300-700 °C, while in wet N₂ a slightly lower value was observed. Among the compounds investigated in the present study Ba_1.75K_1.25CaNb₂O_9 − δ showed the highest total electrical conductivity of 1 × 10^− 3 S/cm in dry H₂ at 700 °C with an activation energy of 1.28 eV in the temperature range of 300-700 °C.     

Intermittent temperature-programmed desorption study of perovskites used for catalytic purposes

A differential desorption technique, called intermittent temperature-programmed desorption (ITPD), was used to give new insights into the properties of La_1−xSr_xCo_0.8Fe_0.2O₃ perovskites as a contribution to improve their performances with respect to various important application fields such as catalysis, electrocatalysis and solid oxide fuel cells (SOFC). Both ITPD and interrupted TPD (carried out at different heating rates) evidenced two distinct oxygen adsorbed states, desorbing at temperatures lower than 400 °C, corresponding to less than 5% of a compact monolayer of oxide ions. The first one, for low desorption temperatures (lower than 290 °C) exhibits a heat of adsorption (ΔH) distribution from 101 to 121 kJ mol⁻¹. The second one, for higher desorption temperatures (between 290 and 400 °C) corresponds to ΔH = 146 ± 4 kJ mol⁻¹. Additionally, for temperatures higher than 400 °C, we observed a continuous desorption of oxygen species, probably originating from the sub-surface or semi-bulk, with an associated activation energy of desorption ≥175 kJ mol⁻¹.     

The electrodeposition behaviors and magnetic properties of Ni-Co films

Ni-Co films with different compositions and microstructures were produced on ITO glasses by electrodeposition from sulphate bath at 25 °C. Cyclic voltammograms give a result that the increase in the Co²⁺ concentration displaces Ni-Co alloy oxidation peaks to negative potential with high Co current distributions. It is observed that the content of cobalt in the films increases from 22.42% to 56.09% as the molar ratio of CoSO₄/NiSO₄ varying from 0.015/0.085 to 0.045/0.055 in electrolyte. XRD patterns reveal that the structure of the films strongly depends on the Co content in the deposited films. The saturation magnetization (M_s) moves up from 144.84 kA m⁻¹ to 342.35 kA m⁻¹ and coercivity (H_c) falls from 15.27 kA m⁻¹ to 7.27 kA m⁻¹ with the heat treatment temperature increasing from 25 °C to 450 °C. The saturation magnetization (M_s) and coercivity (H_c) move up from 340.97 kA m⁻¹ and 7.98 kA m⁻¹ to 971.58 kA m⁻¹ and 18.62 kA m⁻¹ with the Co content increasing from 22.42% to 56.09% after annealing at 450.     

Tailoring mixed proton-electronic conductivity of BaZrO3 by Y and Pr co-doping for cathode application in protonic SOFCs

BaZr_0.8 − xPr_xY_0.2O_3 − δ (BZPYx, 0.1 ≤ x ≤ 0.4) perovskite oxides were investigated for application as cathode materials for intermediate temperature solid oxide fuel cells based on proton conducting electrolytes (protonic-SOFCs). The BZPYx reactivity with CO₂ and water vapor was evaluated by thermogravimetric and X-ray diffraction analyses, and good chemical stability was observed for each BZPYx composition. Conductivity measurements of BZPYx sintered pellets were performed as a function of temperature and p_O2 in humidified atmospheres, corresponding to cathode operating condition in protonic-SOFCs. Different conductivity values and activation energies were measured depending on the Pr content, suggesting the presence of different charge carriers. For all the compositions, the partial electronic conductivity, calculated from conductivity measurements at different p_O2, increased with increasing the temperature from 500 to 700 °C. Furthermore, the larger the Pr content, the larger the electronic conductivity. BaZr_0.7Pr_0.1Y_0.2O_3 − δ and BaZr_0.4Pr_0.4Y_0.2O_3 − δ showed mostly pure proton and electron conductivity, respectively, whereas the intermediate compositions showed mixed proton/electronic conductivity. Among the two mixed proton/electronic conductors, BaZr_0.6Pr_0.3Y_0.2O_3 − δ presented the larger conductivity, which coupled with its good chemical stability, makes this perovskite oxide a candidate cathode materials for protonic-SOFCs.     

Reverse micelle synthesis of perovskite oxide nanoparticles

La_0.6Sr_0.4Co_xFe_1−xO_3−δ (LSCF), La_0.6Sr_0.4Cu_0.2Fe_0.8O_3−δ, Ba_0.5Sr_0.4Co_0.8Fe_0.2O_3−δ and LaFeO_3−δ nanoparticles were synthesized by a reverse micelle procedure. Controlling the size of the micelles through the water:oil phase ratio enabled synthesis of phase pure perovskite particles with average sizes from 14 nm to 50 nm. Small amounts of an impurity phase, likely cobalt oxide, were detected in the XRD spectrum of high cobalt content samples of LSCF (x = 0.8). La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ nanoparticles were utilized to coat the surface of a dense thin-film La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ solid oxide fuel cell cathode. The polarization resistance of the nanoparticle coated electrode, measured at open circuit in air at 973 K, was 20% lower than an equivalent un-coated electrode.     

Chemomechanical properties and microstructural stability of nanocrystalline Pr-doped ceria: An in situ X-ray diffraction investigation

The chemomechanical properties and microstructural stability of nanocrystalline Pr_xCe_1 − xO_2 − δ solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O₂) ~ 200 mbar. The chemical expansion coefficient of nanocrystalline powder specimens, operative at intermediate temperatures during which Pr⁴⁺ is reduced to Pr³⁺, is found to be similar to that obtained for coarse-grained Pr_xCe_1 − xO_2 − δ. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which Pr_xCe_1 − xO_2 − δ is highly oxygen deficient, was found to be greater than that measured for fully oxidized Pr_xCe_1 − xO_2 − δ, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline Pr_xCe_1 − xO_2 − δ is observed to have excellent stability at working temperatures below 800 °C, enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices.     

Impact of synthesis technique on the structure and electrochemical characteristics of Pr0.6Sr0.4Co0.2Fe0.8O3 − δ (PSCF) cathode material

Effect of preparation method for Pr_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ (PSCF) on its electrochemical performance was investigated. Powder samples were synthesized by hexamethylenetetramine (HMTA) and EDTA-citric acid (EC) techniques, respectively. The particles synthesized by HMTA were smaller than those prepared by EC method as proved by TEM. X-ray photoelectron spectroscopy illuminated that more oxygen sites including oxygen vacancy on the surface of HMTA-derived PSCF exist than that of EC-derived PSCF. The area specific resistance (ASR) value of HMTA-derived PSCF cathode was as low as 0.454 Ω cm² at 600 °C, whereas the ASR value of EC-derived PSCF was 0.641 Ω cm². The results in the present study demonstrated the advantages of the HMTA method in the synthesis of highly catalytic active PSCF oxide powder for SOFCs.     

Synthesis and characterization of doped apatite-type lanthanum silicates for SOFC applications

A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La_9.83Si_{6 ‐ x ‐ y}Al_xFe_yO_26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10^− 2 S cm^− 1, was observed for the La_9.83Si₅Al_0.75Fe_0.25O_26 ± δ electrolyte. La_9.83Si_4.5Fe_1.5O_26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.