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Photovoltaic devices are expected to display peak performance if fabricated with perfect single crystals. Since surfaces break the periodicity of a single crystal, there are regions of defects, which give rise to states inside the forbidden energy gap. In polycrystalline thin films, the main structural defect is the grain boundary. The presence of grain boundaries affects the optical absorption, carrier mobility and lifetime of the semiconductor. This review focuses on grain boundary passivation in thin film photovoltaic devices based on copper chalcogenides. Achieving enhanced performance in copper chalcogenide thin film Photovoltaic devices requires effective grain boundary passivation. This approach aims to mitigate the adverse effects of grain boundaries on the optoelectronic properties of the material, leading to improved efficiency and stability in Photovoltaic devices. The abstract discusses recent developments, methodologies and outcomes related to grain boundary passivation strategies, shedding light on their significance in advancing the performance of copper chalcogenide thin film Photovoltaic devices. The exploration of grain boundary passivation in this context contributes valuable insights to the ongoing efforts in optimizing the performance of thin film Photovoltaic technologies.

The complex arrangements of atoms near grain boundaries are difficult to understand theoretically. We propose a phenomenological (Ginzburg–Landau-like) description of crystalline phases based on symmetries and some fairly general stability arguments. This method allows a very detailed description of defects at the lattice scale with virtually no tunning parameters, unlike the usual phase-field methods. The model equations are directly inspired from those used in a very different physical context, namely, the formation of periodic patterns in systems out-of-equilibrium (e.g. Rayleigh–Bénard convection, Turing patterns). We apply the formalism to the study of symmetric tilt boundaries. Our results are in quantitative agreement with those predicted by a recent crystallographic theory of grain boundaries based on a geometrical quasicrystal-like construction. These results suggest that frustration and competition effects near a defect in crystalline arrangements have some universal features, of interest in solids or other periodic phases.

Samples of CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by solid state reaction method. X-ray diffraction analysis confirmed single phase formation for the powder calcined at 1173 K. Sintering was done at different temperatures viz. 1348 K, 1373 K and 1398 K with a fixed heating rate of 3 K/min. Detailed study of dielectric properties was carried out for the CCTO samples sintered at 1373 K for different duration of holding times (2 h and 10 h). It is found that dielectric properties are sensitive to both sintering time and temperature. With increasing sintering time from 2 h to 10 h dielectric constant increases from ∼2.1 × 10⁴ to ∼2.5 × 10⁴ measured at 1 kHz at room temperature. Impedance spectroscopy has been used for separating out of grain and grain boundary contributions to the overall electrical properties.

A continuum field model describing the electrical characteristics of polycrystalline semiconductors ceramics is suggested. Taking into account the continuum theory, a static differential equation about electron level on the base of Poisson equation is established. The one-dimensional calculation is carried out using the Runge–Kutta method. The effect of grain size, temperature and donor concentration on the current–voltage characteristic and specific capacitance of the material is calculated quantitatively using ZnO ceramics as an example. The results pointed out that current and voltage characteristics divide into three regions: Linear region before breakdown field, nonlinear region near breakdown field and upturn region after breakdown field. As the applied voltage increases, the grain boundary barrier and the grain boundary capacitance in the nonlinear zone drop drastically. The results are compared with experimental data. An interesting phenomenon is that the Schottky barrier has a small offset along the direction of the applied electric field.

Polycrystalline La_0.93Sb_0.07MnO₃ ceramics were synthesized using solid-state reaction method. The samples were sintered at different temperatures ranging from 1100°C to 1200°C. It is observed that microstructural, transport and magnetic properties of La_0.93Sb_0.07MnO₃ compounds strongly depend on sintering temperatures (T_S). With T_S increasing, the degree of lattice distortion has been weakened, the grain size has become larger and grain boundaries have decreased. Furthermore, the resistivity was reduced, and metal–insulator transition temperature was enhanced; the saturation magnetization per unit mass has decreased with T_S increasing. These effects of different T_S on physical properties can be explained by the structure distortion and grain boundary contributions for La_0.93Sb_0.07MnO₃ compounds.

In this study, the dielectric response of Potassium (K${}^{+}$)-doped magnesium aluminates nanoparticles (Mg${}_{1-x}$K${}_x$Al₂O₄, x = 0.0, 0.25, 0.5, 0.75, 1.0) have been investigated as a function of frequency (20 Hz to 2 MHz) at room-temperature. Interestingly, the behavior of dielectric constant indicated the ionic or space charge polarization in the low-frequency range and it remains almost constant at high frequency. However, the value of conductivity increases at higher frequencies which is consistent with the previously reported results for the parent compound MgAl₂O₄. Moreover, the Cole–Cole plots represent various relaxation phenomena reflecting the existence of grain (boundaries) resistance effects.

The signature of the anisotropic superconducting order parameter ($\mathrm{\Delta }$) in heavily boron-doped nanocrystalline diamond (BNCD) films is demonstrated from the low-temperature resistivity and magnetoresistance measurements. Due to the presence of boron acceptors predominantly at the well-aligned grain boundaries, Rashba-type spin-orbit coupling can arise which influences the superconducting properties of these films. The one-dimensional (1D) filamentary channels of the grain boundaries suggest the modulation of the $\mathrm{\Delta }$ which explains the peaks observed in the temperature-dependent resistance. This also explains the oscillatory magnetoresistance as a function of the magnetic fields and their angle dependence. From the observed superlattice-like microstructure of the BNCD films, a possible mechanism for creating Fulde–Ferrel and Larkin–Ovchinnikov (FFLO)-type state and chiral vortex lines from the superposition of multiple (Andreev) bound states is discussed. Overall, the interface states of the diamond films can be explained by the well-known Su-Schrieffer-Heeger “soliton” model which is supported by the observation of a zero-bias conductance peak.

The composites with the nominal composition of (1-x)La_0.67Sr_0.33MnO₃ (LSMO)/xCeO₂ were fabricated by the sol–gel method. A special electrical transport behavior is observed in the ρ/ρ_Tp versus temperature curves, where ρ_Tp is the peak resistivity at the insulator–metal transition temperature (T_p). The curves for all samples with different CeO₂ content are parallel in the high-T insulator regime and in a certain temperature range below T_p. Furthermore, a series of parallel straight lines can be found in the versus temperature curves for the samples with different CeO₂ content. By considering the surface magnetization at the grain boundary, we obtain a simple expression for the temperature dependence of resistivity that can reproduce the experimental data in the high-T insulator regime and in a certain temperature range below T_p.

Quartz grain boundaries from metamorphic and igneous rocks may emphasize a complex geometry, characterized by self-similarity over one to two orders of magnitude. Their fractal analysis highlights scaling sub-domains, i.e. scale intervals with a particularly good correlation. Given the importance of these aspects for the deciphering of geological microstructures, the paper is dedicated to the detection and the objective depiction of the features of heterogeneous scaling intervals. A fractal analysis based on the divider method was followed by processing methods that (i) offer a global evaluation of the curve geometry from the point of view of the correlation sub-domains, and (ii) allow a local characterization of the curves in terms of scale, with special concern for the scaling intervals heterogeneity. The application of the proposed approach was exemplified both on natural and synthetic curves. On one hand, the grain boundary analysis highlighted scaling sub-domains most obviously in the case of microstructures that were subject to overprinting, due to successive processes. On the other hand, a pattern superposition in the case of the synthetic curves strongly emphasized scaling sub-domains, as compared to the unperturbed (recursively generated) curve geometry. These aspects were expressed quantitatively and highlighted in more detail on isocorrelation maps. The importance of a rigorous characterization of these sub-domains and, eventually, the detection of pattern overprinting phenomena in geological microstructures emphasize the relevance of such an approach.

The microstructural modifications due to high energy electrons (8–18 MeV) and their correlation with the yielding behavior of polycrystalline nickel have been investigated. The specimens in the form of strips were irradiated at room temperature for 15 min in the energy range 8–18 MeV using linear accelerator. The comparison of microstructural results of irradiated specimens with that of the un-irradiated ones reveals that radiation deteriorate the surface of the target specimens. The damage was found to be more prominent at the grain boundaries. The tensile tests of both unirradiated and irradiated samples were carried out using Universal Testing Machine at room temperature. An increase in yield stress and loss of ductility was observed in case of irradiated specimens, which became more pronounced with an increase of incident beam energy. These effects are attributed to the interaction of glide dislocations stress fields with the defects produced during irradiation.

This study characterizes the microstructure changes of Inconel 718 (IN718) by laser cladding (LC). Well-bonded pore-free, crack-free, single-layer, and multi-layer (overlapped) LC was done on IN718 with the same powder. The basic microstructure illustrates the presence of $\gamma$, $\delta$, and ${\gamma }^{\prime \prime }$ -phases. The precipitation of an irregularly shaped laves phase was observed with dendritic grains in the top and bottom regions of the single-track LC. Further, the epitaxial grain growth of columnar dendrites was observed in the interdendritic region along the laves phase. High leveraging of quick-dissolving behaviors of the laves phase in multi-track LC enhances the high-temperature mechanical performance. Modified grain morphology of the multi-track LC in terms of size, shape, and orientation is reported. Columnar dendrites (short and long) are the most common grains, with varied sizes and orientations reported in line with the Marangoni effect. The microhardness at the top layer of single and multi-track exhibited a higher value of 490.6HV and 500.7HV, respectively, which is comparatively lower than the bottom layer of single and multi-track samples. The influencing process parameter over clad width is scan speed, and over clad height is powder feed. The nonlinear mathematical model is proposed with a reliability of 99.22% and 99.52% for clad width and height, respectively.

We setup a dislocation dynamics finite element framework by bridging a dislocation dynamics program and an open source finite element program. As part of initial verification, deformation of single crystal micro-pillar having single and double glide activation is demonstrated. A case study of a twin boundary is presented wherein the dislocation pile-up at the grain boundary and formation of a residual dislocation are shown. For studying the dislocation interactions with other grain boundaries, model grain boundaries are considered. We consider three synthetic grain boundaries namely transparent, semi-transparent, and impenetrable. The model’s transparent and semi-transparent grain boundaries contain no dislocations and very low density of dislocations in them, respectively, and thus low number of interactions with other dislocations. More junctions and cross-slip occurrences are recorded near the semi-transparent grain boundary. The most dislocation–dislocation interactions near grain boundaries result into glissile junctions. The current results are compared against literature data and it is observed that other than junction formation, cross-slip is very frequency observed near grain boundaries.

Many aspects in the chemical vapor deposition (CVD) growth of graphene remain unclear such as its behavior near the catalyst grain boundaries. Here we investigate the CVD growth mechanism of graphene across the Cu grain boundaries using unidirectional aligned graphene domains, which simplifies the analysis of both graphene and Cu to a large extent. We found that for a graphene domain grown across the Cu grain boundary, the domain orientation is determined by the Cu grain where the domain nucleation center is located, and the Cu grain boundary will not change the growth behavior for this graphene domain. This growth mechanism is consistent with the Cu-step-attached nucleation and edge-attachment-limited growth mechanism for H-terminated graphene domains and will provide more guidance for the synthesis of high-quality graphene with less domain boundaries.

In this study, the effect of Mn on α to γ transformation in the nanostructured high nitrogen Fe-18Cr-xMn stainless steel produced by mechanical alloying (MA) was investigated. MA was performed under nitrogen atmosphere using a high-energy planetary ball mill. X- ray diffraction (XRD) patterns of produced samples showed that α to γ transformation starts after 20 hours of milling and propagates by increasing the milling time. Completion of this phase transformation occurred in the Fe-18Cr-8Mn sample after 100 hours of milling. But, in the Fe-18Cr-7Mn sample, some α phase remained even after 150 hours of milling. Also, nitrogen analysis revealed that nitrogen solubility in the milled powders increased significantly by increasing the milling time, and ultimately reached 1wt%. This is believed to be due to the increase of the lattice defects and development of nanostructure through MA. Variations in grain size and internal lattice strain versus milling time in both cases showed that the critical ferrite grain size for austenite nucleation was lower than 10nm. Moreover, a lower transformation rate was found in samples containing lower Mn content.

Various compositions with x=0.01, 0.05, 0.10, 0.20 and 0.30 in the system SrTi_1-xMn_xO₃ were prepared by solid state ceramic route. Compositions with x ≤ 0.10 were found to be single phase solid solution. In this paper, the result of investigations on the effect of manganese substitution in SrTiO₃ on dielectric behaviour for the compositions with x ≤ 0.10, which form single phase solid solution have been reported. Average grain size is small, this may be due to segregation of dopant at grainboundaries. Dielectric measurements were made in the temperature range 150–500K. Measurements of dielectric properties show that there is not much space charge polarisation across the grains and grainboundaries interface. This space charge polarisation only occurs at high temperature and one observes large dispersion of dielectric constant and dissipation factor. At low temperatures, dielectric behaviour follows the character of SrTiO₃ with only difference in the values of dielectric constant.

A novel lead zinc titanate tungsten oxide (PbZn${}_{1∕3}$Ti${}_{1∕3}$W${}_{1∕3}$O${}_3)$ single perovskite was synthesized employing a cost-effective solid-state reaction technique. A phase transition occurs from tetragonal (P4mm) to monoclinic (C2/m) after substituting zinc (Zn) and tungsten (W) into the B-site of the pure lead titanate. The average crystallite size and micro-lattice strain are 66.2nm and 0.159%, respectively, calculated by the Williamson–Hall method. The grains are uniformly distributed through well-defined grain boundaries and the average grain size is about 17.8$\mu$m analyzed from the SEM micrograph. Raman spectrum suggests the presence of all constituent elements in the sample. The UV–Visible study suggests that the sample is suitable for photovoltaic applications because of high bandgap energy $E_g=4.17$eV. The dielectric study confirms the negative temperature coefficient resistance (NTCR) behavior of the sample. The activation energy increases from 13.9meV to 142meV with a rise of temperature suggesting that ac conductivity is thermally activated. The thermally activated relaxation process was managed by immobile charge carriers at low temperatures while defects and oxygen vacancies at higher temperatures. The presence of the asymmetrical curves in modulus plots confirms the non-Debye-type behavior. Both Nyquist and Cole–Cole semi-circular arcs confirm the semiconductor nature of the sample.

In this communication, the synthesis (solid-state sintering) and characterization of a double perovskite BiFeMoO₆ are reported. Analysis of X-ray diffraction (XRD) data provides monoclinic crystal symmetry with an average crystallite size of 85.6nm and lattice strain of 0.00078, respectively. The microstructural analysis of the sample was done using a scanning electron microscope (SEM) and the results show that grains are well-grown and distributed uniformly throughout the sample surface. The grains are visible clearly due to well-defined grain boundaries, and the effect on the mechanism of electrical ac conductivity was studied. The compositional purity of the sample was checked by energy dispersive X-ray (EDX) analysis spectrum which supports the presence of all constituent elements (Bi, Fe, Mo and O) in both weight and atomic percentages. The study of the Ultraviolet–Visible spectrum provides a bandgap energy of 1.8eV, suitable for photovoltaic applications. The measurements of the dielectric were used to confirm the existence of the Maxwell–Wagner type of dispersion. The study of impedance spectroscopy helps to understand the negative temperature coefficient of resistance (NTCR) character while the electrical modulus measurements claimed a non-Debye relaxation mechanism in the sample. The study of ac conductivity reveals the fact of thermally activated conduction mechanism in the sample. The presence of the semiconducting nature of the sample was checked from both Nyquist plots and Cole–Cole plots. The study of the resistance versus temperature reveals the fact of negative temperature coefficient (NTC) thermistor character and is suitable for some temperature sensor devices.

This paper presents a detailed synthesis method by solid-state reaction route and typical characterization (structural, microstructural, dielectric, impedance, modulus, and optical properties) of a double perovskite material Bi₂FeMn${}_{0.9}$Ce${}_{0.1}$O₆. An orthorhombic crystal structure having an average crystallite size of 32.2nm is suggested by X-ray diffraction data (XRD). Scanning electron microscope (SEM) micrograph detects the presence of cylindrical nanorod-shaped distinct grains and well-defined grain boundaries in this material and the average grain size is 5.82$\mu$m. Furthermore, the purity and the presence of all constituent elements in the material were confirmed from energy dispersive X-ray (EDX) analysis and color mapping. Dielectric, impedance, modulus, and AC conductivity properties are studied within the temperature range of 25–500^∘C and frequency range of 1kHz to 1MHz. The high dielectric constant at a low-frequency zone and low dielectric loss found in this material make it a promising candidate for better energy-storing devices. The negative temperature coefficient of resistance (NTCR) behavior is observed from the impedance study. The non-Debye relaxation is detected in the modulus study. The semiconducting nature of this material is verified by semicircular arcs observed in both Nyquist and Cole–Cole plots. The thermally activated conduction mechanism is confirmed by an AC conductivity study. The existence of Bi–O, Fe–O, Mn–O and Ce–O stretching vibrations are observed from the FTIR study and explain the presence of all constituent elements in the sample. The bandgap energy of 1.7eV is calculated from UV-DRS analysis and hence this material can be used for advanced optoelectronic and photovoltaic applications.