Carbonaceous Materials Porosity Investigation in a Wet State by Low-Field NMR Relaxometry

The porosity of differently wetted carbonaceous material with disordered mesoporosity was investigated using low-field ¹H NMR relaxometry. Spin–spin relaxation (relaxation time T₂) was measured using the CPMG pulse sequence. We present a non-linear optimization method for the conversion of relaxation curves to the distribution of relaxation times by using non-specialized software. Our procedure consists of searching for the number of components, relaxation times, and their amplitudes, related to different types of hydrogen nuclei in the sample wetted with different amounts of water (different water-to-carbon ratio). We found that a maximum of five components with different relaxation times was sufficient to describe the observed relaxation. The individual components were attributed to a tightly bounded surface water layer (T₂ up to 2 ms), water in small pores especially supermicropores (2 < T₂ < 7 ms), mesopores (7 < T₂ < 20 ms), water in large cavities between particles (20–1500 ms), and bulk water surrounding the materials (T₂ > 1500 ms). To recalculate the distribution of relaxation times to the pore size distribution, we calculated the surface relaxivity based on the results provided by additional characterization techniques, such as thermoporometry (TPM) and N₂/−196 °C physisorption.     

Structure and Dielectric Behavior of Yb2O3-MgO Co-Doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 Ferroelectric Relaxor

Dielectric properties and structure of 0.015Yb₂O₃-xMgO doped 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃ ceramics with x = 0.0–0.025 have been investigated. As Yb₂O₃-MgO was added into the BT-NBT, the phase changes from tetragonal to pseudo-cubic, with the tetragonality c/a decreases from 1.011 to 1.008 and XRD peaks broadened. The combined study of XRD and TEM image revealed a formation of core–shell structure in grains with core of 400–600 nm and the shell of a thickness 60–200 nm. There is a slowly phase transition against temperature from the variable temperature Raman analysis. The ferroelectric relaxor peak of BT-NBT decreases from ~4000 to ~2000 and a new broad dielectric peak with an equivalent maximum (ε_r′~2300) appears in the temperature dependent dielectric constant curve (ε_r′-T), which produces a flat ε_r′-T curve. Sample 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃-0.015Yb₂O₃-0.005 MgO and 0.92BaTiO₃-0.08(Na_0.5Bi_0.5)TiO₃-0.015Yb₂O₃-0.01MgO give a ε_r′ variation within ±14% and ±10% in 20–165 °C. The core–shell microstructure should take account for the flattened ε_r′–T behavior of these samples.     

Gd/Mn Co-Doped CaBi4Ti4O15 Aurivillius-Phase Ceramics: Structures,Electrical Conduction and Dielectric Relaxation Behaviors

In this work, Gd/Mn co-doped CaBi₄Ti₄O₁₅ Aurivillius-type ceramics with the formula of Ca_1-xGd_xBi₄Ti₄O₁₅ + xGd/0.2wt%MnCO₃ (abbreviated as CBT-xGd/0.2Mn) were prepared by the conventional solid-state reaction route. Firstly, the prepared ceramics were identified as the single CaBi₄Ti₄O₁₅ phase with orthorhombic symmetry and the change in lattice parameters detected from the Rietveld XRD refinement demonstrated that Gd³⁺ was successfully substituted for Ca²⁺ at the A-site. SEM observations further revealed that all samples were composed of the randomly orientated plate-like grains, and the corresponding average grain size gradually decreased with Gd content (x) increasing. For all compositions studied, the frequency independence of conductivity observed above 400 °C showed a nature of ionic conduction behavior, which was predominated by the long-range migration of oxygen vacancies. Based on the correlated barrier hopping (CBH) model, the maximum barrier height W_M, the dc conduction activation energy E_dc, as well as the hopping conduction activation energy E_p were calculated for the CBT-xGd/0.2Mn ceramics. The composition with x = 0.06 was found to have the highest E_dc value of 1.87 eV, as well as the lowest conductivity (1.8 × 10⁻⁵ S/m at 600 °C) among these compositions. The electrical modules analysis for this composition further illustrated the degree of interaction between charge carrier β increases, with an increase in temperature from 500 °C to 600 °C, and then a turn to decrease when the temperature exceeded 600 °C. The value of β reached a maximum of 0.967 at 600 °C, indicating that the dielectric relaxation behavior at this temperature was closer to the ideal Debye type.     

SAXS Studies of the Endoglucanase Cel12A from Gloeophyllum trabeum Show Its Monomeric Structure and Reveal the Influence of Temperature on the Structural Stability of the Enzyme

Endoglucanases are key enzymes applied to the conversion of biomass aiming for second generation biofuel production. In the present study we obtained the small angle X-ray scattering (SAXS) structure of the G. trabeum endo-1,4-β-glucanase Cel12A and investigated the influence of an important parameter, temperature, on both secondary and tertiary structure of the enzyme and its activity. The CD analysis for GtCel12A revealed that changes in the CD spectra starts at 55 °C and the T_m calculated from the experimental CD sigmoid curve using the Boltzmann function was 60.2 ± 0.6 °C. SAXS data showed that GtCel12A forms monomers in solution and has an elongated form with a maximum diameter of 60 ± 5 Å and a gyration radius of 19.4 ± 0.1 Å as calculated from the distance distribution function. Kratky analysis revealed that 60 °C is the critical temperature above which we observed clear indications of denaturation. Our results showed the influence of temperature on the stability and activity of enzymes and revealed novel structural features of GtCel12A.     

Multi-Response Optimization of Al2O3 Nanopowder-Mixed Wire Electrical Discharge Machining Process Parameters of Nitinol Shape Memory Alloy

Shape memory alloy (SMA), particularly those having a nickel–titanium combination, can memorize and regain original shape after heating. The superior properties of these alloys, such as better corrosion resistance, inherent shape memory effect, better wear resistance, and adequate superelasticity, as well as biocompatibility, make them a preferable alloy to be used in automotive, aerospace, actuators, robotics, medical, and many other engineering fields. Precise machining of such materials requires inputs of intellectual machining approaches, such as wire electrical discharge machining (WEDM). Machining capabilities of the process can further be enhanced by the addition of Al₂O₃ nanopowder in the dielectric fluid. Selected input machining process parameters include the following: pulse-on time (T_on), pulse-off time (T_off), and Al₂O₃ nanopowder concentration. Surface roughness (SR), material removal rate (MRR), and recast layer thickness (RLT) were identified as the response variables. In this study, Taguchi’s three levels L₉ approach was used to conduct experimental trials. The analysis of variance (ANOVA) technique was implemented to reaffirm the significance and adequacy of the regression model. Al₂O₃ nanopowder was found to have the highest contributing effect of 76.13% contribution, T_on was found to be the highest contributing factor for SR and RLT having 91.88% and 88.3% contribution, respectively. Single-objective optimization analysis generated the lowest MRR value of 0.3228 g/min (at T_on of 90 µs, T_off of 5 µs, and powder concentration of 2 g/L), the lowest SR value of 3.13 µm, and the lowest RLT value of 10.24 (both responses at T_on of 30 µs, T_off of 25 µs, and powder concentration of 2 g/L). A specific multi-objective Teaching–Learning-Based Optimization (TLBO) algorithm was implemented to generate optimal points which highlight the non-dominant feasible solutions. The least error between predicted and actual values suggests the effectiveness of both the regression model and the TLBO algorithms. Confirmatory trials have shown an extremely close relation which shows the suitability of both the regression model and the TLBO algorithm for the machining of the nanopowder-mixed WEDM process for Nitinol SMA. A considerable reduction in surface defects owing to the addition of Al₂O₃ powder was observed in surface morphology analysis.     

Polar Order Evolutions near the Rhombohedral to Pseudocubic and Tetragonal to Pseudocubic Phase Boundaries of the BiFeO3-BaTiO3 System

Solid solutions of (1-x)BiFeO₃-xBaTiO₃ (BF-BT, 0.05 ≤ x ≤ 0.98) were prepared and characterized. It was found that the dielectric constant ε_m, remnant polarization P_r and piezoelectric coefficient d₃₃ reach their maximum values near the rhombohedral–pseudocubic phase boundary. In particular, the 0.7BF-0.3BT composition shows large polarization (P_r > 20 μC/cm²) and a temperature-stable piezoelectric property (d₃₃ > 100 pC/N when the annealing temperature is lower than ~400 °C). Near the tetragonal–pseudocubic phase boundary, ε_m and P_r decrease, and the piezoelectric property vanishes when the BF content reaches 4 mol %.     

Microstructures and Electrical Conduction Behaviors of Gd/Cr Codoped Bi3TiNbO9 Aurivillius Phase Ceramic

In this work, a kind of Gd/Cr codoped Bi₃TiNbO₉ Aurivillius phase ceramic with the formula of Bi_2.8Gd_0.2TiNbO₉ + 0.2 wt% Cr₂O₃ (abbreviated as BGTN−0.2Cr) was prepared by a conventional solid-state reaction route. Microstructures and electrical conduction behaviors of the ceramic were investigated. XRD and SEM detection found that the BGTN−0.2Cr ceramic was crystallized in a pure Bi₃TiNbO₉ phase and composed of plate-like grains. A uniform element distribution involving Bi, Gd, Ti, Nb, Cr, and O was identified in the ceramic by EDS. Because of the frequency dependence of the conductivity between 300 and 650 °C, the electrical conduction mechanisms of the BGTN−0.2Cr ceramic were attributed to the jump of the charge carriers. Based on the correlated barrier hopping (CBH) model, the maximum barrier height W_M, dc conduction activation energy E_c, and hopping conduction activation energy E_p were calculated with values of 0.63 eV, 1.09 eV, and 0.73 eV, respectively. Impedance spectrum analysis revealed that the contribution of grains to the conductance increased with rise in temperature; at high temperatures, the conductance behavior of grains deviated from the Debye relaxation model more than that of grain boundaries. Calculation of electrical modulus further suggested that the degree of interaction between charge carriers β tended to grow larger with rising temperature. In view of the approximate relaxation activation energy (~1 eV) calculated from Z″ and M″ peaks, the dielectric relaxation process of the BGTN−0.2Cr ceramic was suggested to be dominated by the thermally activated motion of oxygen vacancies as defect charge carriers. Finally, a high piezoelectricity of d₃₃ = 18 pC/N as well as a high resistivity of ρ_dc = 1.52 × 10⁵ Ω cm at 600 °C provided the BGTN−0.2Cr ceramic with promising applications in the piezoelectric sensors with operating temperature above 600 °C.     

Influence of Different Thermal Aging Conditions on Soot Combustion with Catalyst by Thermogravimetric Analysis

Diesel particulates are deposited in the diesel particulate filter and removed by the regeneration process. The Printex-U (PU) particles are simulated as the diesel soot to investigate the influence of thermal aging conditions on soot combustion performance with the addition of catalysts. The comprehensive combustion index S, combustion stability index R_w and peak temperature T_p are obtained to evaluate the combustion performance. Compared with the PU/Pt mixtures of different Pt contents (2 g/ft³, 3.5 g/ft³, and 5 g/ft³), the 10 g/ft³ Pt contents improve soot combustion with the outstanding oxygen absorption ability. When the weight ratio of PU/Pt mixture is 1:1, the promoted effect achieves the maximum degree. The S and R_w increase to 8.90 × 10⁻⁸ %²min⁻²°C⁻³ and 39.11 × 10⁵, respectively, compared with pure PU. After the thermal aging process, the PU/Pt mixture with a 350 °C aging temperature for 10 h promotes the soot combustion the best when compared to pure PU particles. It is not good as the PU/Pt mixture without aging, because the inner properties of soot and Pt/Al₂O₃ catalyst may have been changed. The S and R_w are 9.07 × 10⁻⁸ %²min⁻²°C⁻³ and 38.39 × 10⁵, respectively, which are close to the no aging mixture. This work plays a crucial role in understanding the mechanism of the comprehensive effect of soot and catalyst on soot combustion after the thermal aging process.     

Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi4Ti4O15 High-Temperature Piezoelectric Ceramics

In this work, SrBi₄Ti₄O₁₅ (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd₂O₃, CeO₂, MnO₂ and Cr₂O₃) were fabricated by a conventional solid-state reaction route. The effects of oxide additives on the phase structures and electrical properties of the SBT ceramics were investigated. Firstly, X-ray diffraction analysis revealed that all these oxides-modified SBT ceramics prepared presented a single SrBi₄Ti₄O₁₅ phase with orthorhombic symmetry and space group of Bb21m, the change in cell parameters indicated that these oxide additives had diffused into the crystalline lattice of SBT and formed solid solutions with it. The SBT ceramics with the addition of MnO₂ achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd₂O₃ could increase the T_C of SBT. At a low frequency of 100 Hz, those dielectric loss peaks appearing around 500 °C were attributed to the space-charge relaxation as an extrinsic dielectric response. The synergetic doping of CeO₂ and Cr₂O₃ could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr₂O₃ can significantly enhance both d₃₃ and k_p of SBT, and produce a higher phase-angle maximum at resonance. Such an enhanced piezoelectricity was attributed to the further increased orthorhombic distortion after Ti⁴⁺ at B-site was substituted by Cr³⁺. Among these compositions, Sr_0.92Gd_0.053Bi₄Ti₄O₁₅ + 0.2 wt% Cr₂O₃ (SGBT-Cr) presented the best electrical properties including T_C = 555 °C, tan δ = 0.4%, k_p = 6.35% and d₃₃ = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d₃₃ was decreased by only 3.6% after being annealed at 500 °C for 4 h. Such advantages provided this material with potential applications in the high-stability piezoelectric sensors operated below 500 °C.     

Evolution of Microstructure in Welding Heat-Affected Zone of G115 Steel with the Different Content of Boron

Welding thermal simulation was performed to investigate the effects of boron content (0, 60, and 130 ppm), welding peak temperature (T_p), and cooling time from 800 to 500 °C (t_8/5) on the microstructure, carbide, subgrain, and microhardness of heat-affected zone (HAZ) in G115 steel. According to the experimental results, the microstructure of coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), inter-critical HAZ (ICHAZ), and sub-critically HAZ (SCHAZ) was martensite, martensite containing a small amount of undissolved carbide, martensite, and over-tempered martensite, tempered martensite, respectively. The presence of B element improved the thermal stability of M₂₃C₆ carbide, thereby resulting in a greater amount of undissolved carbides with a larger diameter in the materials with higher B content under the same T_p. Element B is effective in improving A_c1 and A_c3 for the material. Besides, compared with the material without and containing 60 ppm B, the A_c1 and A_c3 of the material containing 130 ppm B increased by 95 and 108 °C, 69 and 77 °C, respectively. Meanwhile, the FGHAZ area of the material containing 130 ppm B was significantly lower than the material without or containing 60 ppm B, indicating that element B can significantly reduce the formation range of FGHAZ. The alloy content in austenite of ICHAZ of materials without or containing 60 ppm B increased, compared with CGHAZ, its M_s and M_f declined by 50 and 7 °C, 46 and 7 °C, respectively. In contrast, the alloy content in austenite of the material with 130 ppm B content decreases, its M_s and M_f was 37 °C and 32 °C higher than CGHAZ, respectively. The microhardness of HAZ was ranked in descending order as CGHAZ, FGHAZ, ICHAZ, and SCHAZ. Differently, the microhardness of CGHAZ and FGHAZ showed an increasing trend with the rise of B content but exhibited a decreasing trend with the rise of t_8/5.     

Tailoring the Stability of Ti-Doped Sr2Fe1.4TixMo0.6−xO6−δ Electrode Materials for Solid Oxide Fuel Cells

In this work, the stability of Sr₂(FeMo)O_6−δ-type perovskites was tailored by the substitution of Mo with Ti. Redox stable Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ (x = 0.1, 0.2 and 0.3) perovskites were successfully obtained and evaluated as potential electrode materials for SOFCs. The crystal structure as a function of temperature, microstructure, redox stability, and thermal expansion properties in reducing and oxidizing atmospheres, oxygen content change, and transport properties in air and reducing conditions, as well as chemical stability and compatibility towards typical electrolytes have been systematically studied. All Sr₂Fe_1.4Ti_xMo_0.6−xO_6−δ compounds exhibit a regular crystal structure with Pm-3m space group, showing excellent stability in oxidizing and reducing conditions. The increase of Ti-doping content in materials increases the thermal expansion coefficient (TEC), oxygen content change, and electrical conductivity in air, while it decreases the conductivity in reducing condition. All three materials are stable and compatible with studied electrolytes. Interestingly, redox stable Sr₂Fe_1.4Ti_0.1Mo_0.5O_6−δ, possessing 1 μm grain size, low TEC (15.3 × 10⁻⁶ K⁻¹), large oxygen content change of 0.72 mol·mol⁻¹ between 30 and 900 °C, satisfactory conductivity of 4.1–7.3 S·cm⁻¹ in 5% H₂ at 600–800 °C, and good transport coefficients D and k, could be considered as a potential anode material for SOFCs, and are thus of great interest for further studies.     

Elaboration of Alumina-Zirconia Composites: Role of the Zirconia Content on the Microstructure and Mechanical Properties

Alumina-zirconia (AZ) composites are attractive structural materials, which combine the high hardness and Young’s modulus of the alumina matrix with additional toughening effects, due to the zirconia dispersion. In this study, AZ composites containing different amounts of zirconia (in the range 5–20 vol %) were prepared by a wet chemical method, consisting on the surface coating of alumina powders by mixing them with zirconium salt aqueous solutions. After spray-drying, powders were calcined at 600 °C for 1 h. Green bodies were then prepared by two methods: uniaxial pressing of spray-dried granules and slip casting of slurries, obtained by re-dispersing the spray dried granulates. After pressureless sintering at 1500 °C for 1 h, the slip cast samples gave rise to fully dense materials, characterized by a quite homogeneous distribution of ZrO₂ grains in the alumina matrix. The microstructure, phase composition, tetragonal to monoclinic transformation behavior and mechanical properties were investigated and are here discussed as a function of the ZrO₂ content. The material containing 10 vol % ZrO₂ presented a relevant hardness and exhibited the maximum value of K_I0, mainly imputable to the t → m transformation at the crack tip.     

Influence of Slide Burnishing Parameters on the Surface Layer Properties of Stainless Steel and Mean Positron Lifetime

This paper presents the results of an experimental study on the impact of slide burnishing on surface roughness parameters (Sa, Sz, Sp, Sv, Ssk, and Sku), topography, surface layer microhardness, residual stress, and mean positron lifetime (τ_mean). In the study, specimens of X6CrNiTi18 stainless steel were subjected to slide burnishing. The experimental variables were feed and slide burnishing force. The slide burnishing process led to changes in the surface structure and residual stress distribution and increased the surface layer microhardness. After slide burnishing, the analyzed roughness parameters decreased compared with their pre-treatment (grinding) values. The slide burnishing of X6CrNiTi18 steel specimens increased their degree of strengthening e from 8.77% to 42.74%, while the hardened layer thickness g_h increased after the treatment from about 10 µm to 100 µm. The maximum compressive residual stress was about 450 MPa, and the maximum depth of compressive residual stresses was g_σ = 1.1 mm. The positron mean lifetime τ_mean slightly yet systematically increased with the increase in burnishing force F, while an increase in feed led to changes of a different nature.     

Al2O3/ZrO2/Y3Al5O12 Composites: A High-Temperature Mechanical Characterization

An Al₂O₃/5 vol%·ZrO₂/5 vol%·Y₃Al₅O₁₂ (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO₂ and YAG grains dispersed in a sub-micronic alumina matrix. The high temperature mechanical properties were investigated by four-point bending tests up to 1500 °C, and the grain size stability was assessed by observing the microstructural evolution of the samples heat treated up to 1700 °C. Dynamic indentation measures were performed on as-sintered and heat-treated Al₂O₃/ZrO₂/YAG samples in order to evaluate the micro-hardness and elastic modulus as a function of re-heating temperature. The high temperature bending tests highlighted a transition from brittle to plastic behavior comprised between 1350 and 1400 °C and a considerable flexural strength reduction at temperatures higher than 1400 °C; moreover, the microstructural investigations carried out on the re-heated samples showed a very limited grain growth up to 1650 °C.     

The Influence of Oxidation on the Magnetic,Electrical, and Mechanical Properties of Co40Fe40Yb20 Films

A typical body-centered cubic (BCC) CoFe(110) peak was discovered at approximately 2θ = 44.7°. At 2θ = 46°, 46.3°, 47.7°, 55.4°, 54.6°, and 56.4°, the Yb₂O₃ and Co₂O₃ oxide peaks were visible in all samples. However, with a heat treatment temperature of 300 °C, there was no typical peak of CoFe(110). Electrical characteristics demonstrated that resistivity and sheet resistance reduced dramatically as film thickness and annealing temperatures increased. At various heat treatments, the maximum hardness was 10 nm. The average hardness decreased as the thickness increased, and the hardness trend decreased slightly as the annealing temperature was higher. The highest low-frequency alternative-current magnetic susceptibility (χ_ac) value was discovered after being annealed at 200 °C with 50 nm, and the optimal resonance frequency (f_res) was discovered to be within the low-frequency range, indicating that the Co₄₀Fe₄₀Yb₂₀ film can be used in low-frequency applications. The maximum saturation magnetization (Ms) was annealed at 200 °C for 50 nm. Thermal disturbance caused the Ms to decrease as the temperature reached to 300 °C. The results show that when the oxidation influence of as-deposited and thinner films is stronger than annealing treatments and thicker thickness, the magnetic and electrical properties can be enhanced by the weakening peak of the oxide, which can also reduce interference.     

Observation of a multiferroic critical end point

The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a “metaelectric” critical end point, has been rarely studied. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (H) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn₂O₅, in which the electric polarization (P) switches polarity along with a concomitant Mn spin–flop transition at a critical magnetic field H_c. The simultaneous metaelectric and spin–flop transitions become sharper upon cooling but remain a continuous cross-over even down to 0.5 K. Near the P = 0 line realized at μ₀H_c ≈ 18 T below 20 K, the dielectric constant (ɛ) increases significantly over wide field and temperature (T) ranges. Furthermore, a characteristic power-law behavior is found in the P(H) and ɛ(H) curves at T = 0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn₂O₅ near zero temperature.     

Flexural Response and Failure Analysis of Solid and Hollow Core Concrete Beams with Additional Opening at Different Locations

It is essential to make openings in structural concrete elements to accommodate mechanical and electrical needs. To study the effect of these openings on the performance of reinforced concrete (RC) elements, a numerical investigation was performed and validated using previous experimental work. The effect of the position and dimension of the opening and the beam length on the response of the beams, loads capacities, and failure modes was studied. The simulated RC beams showed different responses, loads capacities, and failure modes depending on the position and dimension of the opening. The transversal near support opening (TNSH) and longitudinal holes (LH) showed lower effects on the load capacities of the beams than the transversal near center opening (TNCH). The supreme reduction percentages of the load capacity (µ_u%) for beams with TNCH and TNSH were 37.21% and 30.34%, respectively (opening size = 150 × 150 mm²). In addition, the maximum µ_u% for beam with LH was 17.82% (opening size = 25% of the beam size). The TNSH with a width of less than 18.18% of the beam shear span (550 mm) had trivial effects on the beam’s load capacities (the maximum µ_u% = 1.26%). Although the beams with combined LH and TNCH or LH and TNSH showed different failure modes, they experienced nearly the same load reductions. Moreover, the length of the beam (solid or hollow) had a great effect on its failure mode and load capacity. Finally, equations were proposed and validated to calculate the yield load and post-cracking deflection for the concrete beams with a longitudinal opening.     

D-π-A-Type Pyrazolo[1,5-a]pyrimidine-Based Hole-Transporting Materials for Perovskite Solar Cells: Effect of the Functionalization Position

Donor–acceptor (D–A) small molecules are regarded as promising hole-transporting materials for perovskite solar cells (PSCs) due to their tunable optoelectronic properties. This paper reports the design, synthesis and characterization of three novel isomeric D-π-A small molecules PY1, PY2 and PY3. The chemical structures of the molecules consist of a pyrazolo[1,5-a]pyrimidine acceptor core functionalized with one 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole (3,6-CzDMPA) donor moiety via a phenyl π-spacer at the 3, 5 and 7 positions, respectively. The isolated compounds possess suitable energy levels, sufficient thermal stability (T_d > 400 °C), molecular glass behavior with T_g values in the range of 127–136 °C slightly higher than that of the reference material Spiro-OMeTAD (126 °C) and acceptable hydrophobicity. Undoped PY1 demonstrates the highest hole mobility (3 × 10⁻⁶ cm² V⁻¹ s⁻¹) compared to PY2 and PY3 (1.3 × 10⁻⁶ cm² V⁻¹ s⁻¹). The whole isomers were incorporated as doped HTMs in planar n-i-p PSCs based on double cation perovskite FA_0.85Cs_0.15Pb(I_0.85Br_0.15)₃. The non-optimized device fabricated using PY1 exhibited a power conversion efficiency (PCE) of 12.41%, similar to that obtained using the reference, Spiro-OMeTAD, which demonstrated a maximum PCE of 12.58% under the same conditions. The PY2 and PY3 materials demonstrated slightly lower performance in device configuration, with relatively moderate PCEs of 10.21% and 10.82%, respectively, and slight hysteresis behavior (−0.01 and 0.02). The preliminary stability testing of PSCs is also described. The PY1-based device exhibited better stability than the device using Spiro-OMeTAD, which could be related to its slightly superior hydrophobic character preventing water diffusion into the perovskite layer.     

Role of SiNx Barrier Layer on the Performances of Polyimide Ga2O3-doped ZnO p-i-n Hydrogenated Amorphous Silicon Thin Film Solar Cells

In this study, silicon nitride (SiN_x) thin films were deposited on polyimide (PI) substrates as barrier layers by a plasma enhanced chemical vapor deposition (PECVD) system. The gallium-doped zinc oxide (GZO) thin films were deposited on PI and SiN_x/PI substrates at room temperature (RT), 100 and 200 °C by radio frequency (RF) magnetron sputtering. The thicknesses of the GZO and SiN_x thin films were controlled at around 160 ± 12 nm and 150 ± 10 nm, respectively. The optimal deposition parameters for the SiN_x thin films were a working pressure of 800 × 10⁻³ Torr, a deposition power of 20 W, a deposition temperature of 200 °C, and gas flowing rates of SiH₄ = 20 sccm and NH₃ = 210 sccm, respectively. For the GZO/PI and GZO-SiN_x/PI structures we had found that the GZO thin films deposited at 100 and 200 °C had higher crystallinity, higher electron mobility, larger carrier concentration, smaller resistivity, and higher optical transmittance ratio. For that, the GZO thin films deposited at 100 and 200 °C on PI and SiN_x/PI substrates with thickness of ~000 nm were used to fabricate p-i-n hydrogenated amorphous silicon (α-Si) thin film solar cells. 0.5% HCl solution was used to etch the surfaces of the GZO/PI and GZO-SiN_x/PI substrates. Finally, PECVD system was used to deposit α-Si thin film onto the etched surfaces of the GZO/PI and GZO-SiN_x/PI substrates to fabricate α-Si thin film solar cells, and the solar cells’ properties were also investigated. We had found that substrates to get the optimally solar cells’ efficiency were 200 °C-deposited GZO-SiN_x/PI.     

On Structural Rearrangements during the Vitrification of Molten Copper

We utilise displacement analysis of Cu-atoms between the chemical bond-centred Voronoi polyhedrons to reveal structural changes at the glass transition. We confirm that the disordered congruent bond lattice of Cu loses its rigidity above the glass transition temperature (T_g) in line with Kantor–Webman theorem due to percolation via configurons (broken Cu-Cu chemical bonds). We reveal that the amorphous Cu has the T_g = 794 ± 10 K at the cooling rate q = 1 × 10¹³ K/s and that the determination of T_g based on analysis of first sharp diffraction minimum (FDSM) is sharper compared with classical Wendt–Abraham empirical criterion.