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Transport in novel materials, specifically those scaled up to wafer sizes, will be dominated by thermionic emission over charged, randomly oriented grain boundaries. However, the challenges presented by random dopant fluctuation in lightly and moderately doped nano-crystalline materials are yet to be addressed. Here, we present a self-consistent model to describe the transport in polycrystalline materials with medium doping levels, where conductivity is governed by thermionic emission over low and wide barriers. We show that random doping fluctuations contribute to a higher material resistivity, which is explained through a non-linear potential drop over the depletion regions on both sides of the boundary. This leads to a decrease in the exponential slope at the onset of conductivity, down to values of ∼ exp ⁡ (− 2.4 kT) − 1 , as well as to asymmetry in the current–voltage characteristics. We demonstrate that the model can be scaled up to several grains and their boundaries, by using commercially available circuit simulators, where non-linearity is realized through look-up tables. We find that an increase in resistivity of up to 18% compared to the nominal, uniformly doped material can be explained simply by the introduction of random dopant fluctuations. [ABSTRACT FROM AUTHOR]

Crystal growth is a complex process with far-reaching implications for high-performance materials across various fields. Recent advancements in structural analysis methods such as polyhedral template matching, which allows semiconductor-specific analysis, coupled with simulation technology, have enabled the comprehensive study of crystallization dynamics in semiconductors. However, the exploration of polycrystalline semiconductors created with minimal external intervention of the crystallization processes is relatively uncharted in comparison with metals. In this study, we employ molecular dynamics to simulate the growth of polycrystalline CdTe/CdS with the assumptions of classical mechanics, a Stillinger–Weber potential, an amorphous substrate, and common vapor growth conditions to allow the polycrystalline structures to evolve naturally. Post-simulation, we identify and analyze impactful structures and events, comparing them to theory and experiment to gain insight into various modes of crystallization dynamics. Two research questions guided the study: (1) How realistic are assumption-less simulated polycrystalline semiconductor structures? (2) To what extent can the approach provide insight into crystallization? The simulations, performed with minimal external control, yield polycrystalline structures mirroring experimental findings. The analysis reveals key crystallization insights, such as the role of amorphous atoms in the transition from nucleation to grain growth and the transformative impact of single events, such as dislocations, on crystallization dynamics. The method paves the way for reproducing and analyzing realistic polycrystalline semiconductor structures with minimal simulation assumptions across various growth modes. [ABSTRACT FROM AUTHOR]

The electrical properties of high‐purity magnesium oxide (MgO) samples sintered between 1500 and 1650°C were investigated up to 800°C. Dielectric constant, loss tangent and electrical conductivity were measured between 25 and 800°C. Optimum electrical properties were obtained for the sample sintered at 1600°C. The impurities in polycrystalline and single crystal MgO were discussed to understand their effect on electrical properties and the role of grain boundaries. Higher dielectric losses of polycrystalline samples as compared to the single crystal MgO were attributed to the presence of grain boundaries. MgO could be a useful dielectric material for capacitor applications up to 600°C. [ABSTRACT FROM AUTHOR]

The application of machine learning in materials science has yielded several benefits, including the prediction of physical properties and the improvement of experimental efficiency. However, with complex models, such as convolutional neural networks (CNN), learning has become a black box, from which no universal physical knowledge can be obtained. In this study, a highly accurate prediction of the electrical properties of polycrystalline semiconductor thin films is achieved by learning multichannel CNN models from electron backscattering diffraction (EBSD) data, that is band contrasts, grain boundaries, and inverse pole figures. In addition, it examines how the CNN model learned the correlation between the crystallinity, grain boundaries, crystallographic orientation, and carrier mobility by polarizing certain EBSD data and checking the predicted changes in carrier mobility. Physical parameters affecting carrier mobility can be extracted, which is challenging via human image recognition. The methods proposed in this study will not only enable the prediction of electrical properties from EBSD data for all materials but also will contribute to the discovery of complex physical phenomena beyond the limits of human analysis. [ABSTRACT FROM AUTHOR]

Material selection for thermoelectric modules and generators presents a considerable challenge. In commercially available thermoelectric generators, alloys with a high percentage of doping element are used to achieve different semiconductor polarity. This introduces mechanical stresses to the system due to the varying thermal expansion rates. Previous studies have demonstrated that the semiconductor polarity of SnSe alloys can be altered through Sb or Bi doping. This paper outlines a modified, scalable and cost-effective direct synthesis process for SnSe alloys, employing Sb, Bi, Ag, Ni, In and Mg as dopants. Polarity switching in the synthesized materials was observed with Bi doping, occurring in similar regions as observed with monocrystalline Sb. Additionally, In doping led to a significant increase in the Seebeck coefficient. Doping elements exhibited minimal influence on the crystal lattice of the material, with only minor shifts in lattice parameters noted. Crystallography analysis revealed a significant preferred orientation, consistent with the material's documented propensity to form and align in layers, a characteristic observable even to the naked eye and confirmed through optical and electron microscopy. Furthermore, we have developed and thoroughly calibrated an in-house apparatus for determining the Seebeck coefficient of thermoelectric materials, based on the already published methodology, which describes a method for determining the electrical conductivity of disk- and rod-shaped samples. [ABSTRACT FROM AUTHOR]

Studying the properties of thermoelectric materials needs substantial effort owing to the interplay of the trade-off relationships among the influential parameters. In view of this issue, artificial intelligence has recently been used to investigate and optimize thermoelectric materials. Here, we used Bayesian optimization to improve the thermoelectric properties of multicomponent III–V materials; this domain warrants comprehensive investigation due to the need to simultaneously control multiple parameters. We designated the figure of merit ZT as the objective function to improve and search for a five-dimensional space comprising the composition of InGaAsSb thin films, dopant concentration, and film-deposition temperatures. After six Bayesian optimization cycles, ZT exhibited an approximately threefold improvement compared to its values obtained in the random initial experimental trials. Additional analysis employing Gaussian process regression elucidated that a high In composition and low substrate temperature were particularly effective at increasing ZT. The optimal substrate temperature (205 °C) demonstrated the potential for depositing InGaAsSb thermoelectric thin films onto plastic substrates. These findings not only promote the development of thermoelectric devices based on III–V semiconductors but also highlight the effectiveness of using Bayesian optimization for multicomponent materials. Bayesian optimization improved the thermoelectric properties of InGaAsSb thin films; this domain warrants comprehensive investigation due to the need to simultaneously control multiple parameters, such as, the composition, dopant concentration, and film-deposition temperatures. After six optimization cycles, the dimensionless figure of merit exhibited an approximately threefold improvement compared to its values obtained in the random initial experimental trials. These findings not only promote the development of thermoelectric devices based on III–V semiconductors but also highlight the effectiveness of using Bayesian optimization for multicomponent materials. [ABSTRACT FROM AUTHOR]

The influence of crystal anisotropy on the micromechanical properties of ceramic grains plays an important role in the design of the macromechanical performance of bulk polycrystalline samples. To this end, the effect of crystal orientation on fracture toughness and strength was investigated by microcantilever bending experiments combined with finite element method (FEM) simulations in grains of a polycrystalline ZrB2 sample. The sample was prepared by hot pressing and the crystal orientations were determined by electron backscatter diffraction after careful surface preparation. The bending tests were carried out on notched and unnotched microcantilevers cut from specific grains along the prismatic (⊥ to c‐axis), basal (∥ to c‐axis), and intermediate (45° to c‐axis) directions of ZrB2 crystals using focused ion beam milling. The fracture toughness and strength were determined by FEM‐derived analytical solutions. The fracture strength was similar with values of about 11–12 GPa in every direction. Enhanced plasticity was found in the intermediate direction of unnotched beams as compared to the other two brittle orientations. The fracture toughness was found to be 30% higher in the intermediate direction (4.1 MPa m0.5) than those measured for the basal (3.1 MPa m0.5) and prismatic directions (3.3 MPa m0.5). These findings were explained by the orientation dependence of slip system activations which provide a new way in the design of textured polycrystalline ZrB2 ceramics toward enhanced damage tolerance. [ABSTRACT FROM AUTHOR]

The structural, optical, morphological, and electrical properties of polycrystalline copper-doped tin sulfide (Cu-Sn2S3) thin films with different concentrations of Cu dopants were synthesized using the spray pyrolysis method. Structural characterizations (powder XRD) revealed orthorhombic Sn2S3 crystal structure with Pmma space group. The XRD spectra showed improved crystalline quality and preferential orientation for the Cu-doped Sn2S3 thin films. Morphology of the prepared samples revealed sharp needle-shaped grains uniformly distributed throughout the sample. The UV spectroscopy results show 70–75% transmittance for 6 wt.% and 8 wt.% Cu-doped Sn2S3 thin films in the visible region. The bandgap values are decreased for the 4 wt.% sample and increased with an increase in the Cu concentration for 2 wt.%, 6 wt.%, and 8 wt.% with Sn2S3 thin films. The dielectric constant, dielectric loss, and electrical and optical properties were analyzed using UV data. Negative Hall coefficient values of prepared samples confirm the n-type semiconductor nature. Electrical conductivity increases with an increase in Cu concentration. These results indicate that the samples have potential applications in the optoelectronic field. [ABSTRACT FROM AUTHOR]

Yttrium iron garnet (YIG: Y3Fe5O12) is an ideal magnetic material with potential applications in microwave and spintronic devices. A key prerequisite for seamless integration into current semiconductor electronics is the growth of high-quality YIG films on substrates beyond isostructural Gadolinium gallium garnet. In this context, we present the successful fabrication of YIG thin films with varying thickness (70 ≤ t ≤ 380) on fused quartz substrates utilizing radio-frequency (rf) magnetron sputtering. The Rietveld refinement of the X-ray diffraction data uncovers the formation of body-centered cubic single-phase polycrystalline YIG with the space group of Ia-3d. Saturation magnetization (4πMS) and coercivity (HC), as determined by the physical property measurement system (PPMS), exhibit a dependence on the film's thickness (t). Remarkably, the film with t = 380 nm shows a 4πMS value of 1775, closely resembling the bulk YIG value, with an exceptionally low coercivity (HC < 5 Oe). From ferromagnetic resonance (FMR) measurements, the estimated effective saturation magnetization (4πMeff) is found to be very much different from the 4πMS obtained from PPMS and is attributed to the presence of stressed-induced magnetic anisotropy (HK) in YIG films. The FMR linewidth (ΔH) of the YIG films is found to be quite sensitive to HK and the minimum ΔH value of 80 Oe is observed in the film with the lowest HK. The findings indicate that YIG films deposited on quartz substrates have potential advantages for their application in semiconductor-integrated devices. Importantly, this study delves into the fundamental intricacies of YIG growth on non-garnet substrates and offers a well-optimized recipe for generating high-quality YIG thin films through RF sputtering. [ABSTRACT FROM AUTHOR]

The polycrystalline sample Bi4Ti2.8Sn0.2O12 was synthesized using the solid-state reaction method at 850 °C. The sample was formed in a single-phase orthorhombic structure and having space group B2ab, according to the XRD study at room temperature. The dielectric behaviors of the sample have been studied for the frequency range 1 kHz-1 MHz and a wide range of temperature 25-500 °C, which provide some important properties of the synthesized sample. The Nyquist plots provide the effect of grains and grain boundaries to the total resistance and capacitance of the synthesized compound. From ac-conductivity studies, various kinds of conduction mechanisms have been examined. The J–E characteristics support the Ohmic character of the prepared sample. The ferroelectric property at room temperature at frequency 50 Hz has been studied from polarization study. [ABSTRACT FROM AUTHOR]

The polycrystalline sample Bi4Ti2.8Sn0.2O12 was synthesized using the solid-state reaction method at 850 °C. The sample was formed in a single-phase orthorhombic structure and having space group B2ab, according to the XRD study at room temperature. The dielectric behaviors of the sample have been studied for the frequency range 1 kHz-1 MHz and a wide range of temperature 25-500 °C, which provide some important properties of the synthesized sample. The Nyquist plots provide the effect of grains and grain boundaries to the total resistance and capacitance of the synthesized compound. From ac-conductivity studies, various kinds of conduction mechanisms have been examined. The J–E characteristics support the Ohmic character of the prepared sample. The ferroelectric property at room temperature at frequency 50 Hz has been studied from polarization study. [ABSTRACT FROM AUTHOR]

Polycrystalline Ni-base superalloys that offer equivalent or superior performance to current commercial alloys at lower overall cost are of widespread industrial interest. In this work, a new polycrystalline Ni-base superalloy with low elemental cost has been characterized and compared to current commercially available alternatives. Through a combination of scanning electron microscopy, thermal analysis, synchrotron X-ray diffraction, and hardness testing, a broad preliminary investigation of fundamental alloy properties has been performed, identifying the key areas for further alloy development opportunities. [ABSTRACT FROM AUTHOR]

Synthesis (via solid-state reaction) and characterization (structure, microstructure, dielectric, electrical, and ferroelectric behavior) of brownmillerite polycrystalline material NaBiFe2O5 (NBFO) are discussed in this paper. The formation of a triclinic structure has been analyzed by the X-ray diffraction method. The morphology of the ceramic sample was analyzed using a field emission scanning electron microscope (FESEM) and energy-dispersive X-ray analysis (EDX). It is found that the grains are uniformly distributed through well-defined grain boundaries of the sample containing all the constituent elements (Na, Bi, Fe, and O). The study of both frequency (1 kHz–1MHz) and temperature (25–450 °C) dependent dielectric and AC-conductivity predicts the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism of NBFO. The impedance spectra support the semiconducting behavior of the brownmillerite NBFO at high temperature. The resistance of the material falls with a rise in temperature favors the negative temperature coefficient resistance behavior of the material. The study of electric polarization suggests the possibility of the ferroelectric properties of the studied sample. The high dielectric constant and low tangent loss suggest the possibility of the material for device applications. [ABSTRACT FROM AUTHOR]

Synthesis (via solid-state reaction) and characterization (structure, microstructure, dielectric, electrical, and ferroelectric behavior) of brownmillerite polycrystalline material NaBiFe2O5 (NBFO) are discussed in this paper. The formation of a triclinic structure has been analyzed by the X-ray diffraction method. The morphology of the ceramic sample was analyzed using a field emission scanning electron microscope (FESEM) and energy-dispersive X-ray analysis (EDX). It is found that the grains are uniformly distributed through well-defined grain boundaries of the sample containing all the constituent elements (Na, Bi, Fe, and O). The study of both frequency (1 kHz–1MHz) and temperature (25–450 °C) dependent dielectric and AC-conductivity predicts the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism of NBFO. The impedance spectra support the semiconducting behavior of the brownmillerite NBFO at high temperature. The resistance of the material falls with a rise in temperature favors the negative temperature coefficient resistance behavior of the material. The study of electric polarization suggests the possibility of the ferroelectric properties of the studied sample. The high dielectric constant and low tangent loss suggest the possibility of the material for device applications. [ABSTRACT FROM AUTHOR]

The solid-state reaction technique was used to produce polycrystalline Bi1−xBaxFe1−x(Zn1/3Nb2/3)xO3 at different substitutions for x = 0, 0.025 and 0.05 (referred to as BFO, BBFZN25, and BBFZN50, respectively). Both x-ray diffraction and Raman spectroscopy revealed that the substitution did not affect the rhombohedral structure of BFO. However, the substitution did not prevent the formation of a second phase, which was identified as Bi25FeO39. The amount of this impurity phase was extracted through Rietveld refinement and was further corroborated by Mössbauer spectroscopy. Lattice parameters were found to be increased owing to substitution of larger ions on average. The substitution not only had an impact on average crystallite size, microstrain and dislocation density of BFO, but also had a significant effect on its dielectric properties. As a result, the dielectric permittivity was enhanced, with a notable reduction in dielectric loss. In particular, the magnitude of dielectric permittivity for the optimal composition BBFZN25 reached a value of 360 at room temperature (RT), which is much greater than that for pure BFO. This higher dielectric constant may be attributable to the larger average crystallite size. The reduction in dielectric loss, at RT, suggests an improvement in the electrical resistivity of BFO, caused by the reduction of the creation of oxygen vacancies and the generation of Fe2+. The non-formation of Fe2+ was verified through Mössbauer spectroscopy. The remarkable increase in the dielectric constant for BBFZN25 at higher temperatures (T > RT) is attributed to the interfacial polarization occurring at grain–grain boundary and internal barrier layers related to the Bi25FeO39 phase. [ABSTRACT FROM AUTHOR]

The necessity of affordable and durable building-integrated photovoltaics has gained widespread importance for the renewable energy transition involving electrification and decarbonization in climate-neutral cities that possess many public health co-benefits. Although the PV market is dominated by polycrystalline and monocrystalline silicon solar cells of the first generation, there is an impetus in the research lately for more sophisticated solar cell architectures with higher efficiency, longer lifetime, and less use of raw materials in an eco-design approach. To accelerate building integration of the next generation of photovoltaics and the associated climate change mitigation benefits, we propose in this work a holistic novel approach to the requirements and associated parameters for the emerging and innovative PV structures, spanning from intrinsic cell properties to panels effect in the urban environment. Within this framework, and supported by building simulation, the improvement of cells' efficiency is revealed as an important parameter for their wider PV building and urban deployment as well as a major improvement in covering the building energy needs with minimized thermal impact in the urban environment. By analyzing the lab-reported values and the timeline of emerging and novel tandem solar cells, we propose the 30% BIPV efficiency of the eco-designed BIPV products as a central milestone to be attained before 2030 for a sustainable urban transformation. [ABSTRACT FROM AUTHOR]

Defect formation during synthesis is one of the strategies used to improve the photoactivity of polycrystalline semiconductors such as titanium dioxide (TiO2). Defects can modify the electronic structure of TiO2 and change the surface of the interaction between the photocatalyst and the reactants. In this study, TiO2 relationship between processing in the presence of iodine and the consequent formation of intrinsic defects were explored. TiO2 nanoparticles were synthesized using the polymeric precursor method and exposed to iodine ions at concentrations up to 5 mol%. After calcination at 350°C, detailed chemical analyses revealed that iodine was absent in the samples. However, the TiO2 properties, such as specific surface area, crystallite sizes, and specific grain boundary area, were affected. Further experiments, such as electron paramagnetic resonance, diffuse reflectance, optical measurements, and electrochemical impedance spectroscopy indicated the presence of defects in the iodine‐processed samples. These defects directly influenced the electrical properties of the material, which affected the photoactivity, measured by the degradation of acetaminophen. [ABSTRACT FROM AUTHOR]

We have prepared a set of polycrystalline samples of PbPd 1 − x − y Fe y Li x O 2 (x = 0 , 0.01, 0.02, 0.03, and 0.04; y = 0 , 0.02, and 0.05) and have measured synchrotron x-ray diffraction and magnetization systematically. We have found high-temperature ferromagnetism in Fe- and Li-substituted samples and the largest magnetic moment of 0.023 μ B per formula unit in PbPd 0.93 Fe 0.05 Li 0.02 O 2. The ferromagnetism survives at 700 K, and the Curie temperature will be far above 800 K. Although similar but controversial high-temperature ferromagnets have been reported in many thin-film samples thus far, the discovered ferromagnetism is macroscopic in the sense that bulk samples stick to a permanent magnet at room temperature. The Fe and Li dependence of the ferromagnetism is complicated, implying that the ferromagnetism is truly unconventional. [ABSTRACT FROM AUTHOR]

In this report, for the first time, Co2U-type hexaferrite (Ba4Co2Fe36O60) nanomaterials have been considered along with their conjugation with a poly(vinylidene fluoride) (PVDF) matrix for the fabrication of heterostructure composite materials with superior electromagnetic interference shielding effectiveness (SE) that can produce better attenuation of microwave radiation. The high value of magnetizations of ∼7.21 and 10.63 emu/g is significant for the improvement of the shielding effectiveness due to absorption (SEA) of the composite materials. The unique combination of magnetic and dielectric responses of these Co2U-type hexaferrite nanomaterials helps to get significantly high total shielding effectiveness (SET) in their PVDF composite states within the frequency range of 8–18 GHz. A very high value of SET of approximately −83 dB at 14.2 GHz with >99.999 999% of attenuation of incident radiation has been observed for the Co2U-type hexaferrite–PVDF composite materials. The β-phase modified PVDF structure also plays the most important role to generate induced polarization inside the structure of composite materials. Also, this PVDF matrix provides the application friendly laminated structure of Co2U-type hexaferrite–PVDF composite materials. Structural, morphological, and chemical studies reveal the presence of the polycrystalline phase of Co2U-type hexaferrite and β-phase crystallization of polar PVDF in the multi-phase Co2U-type hexaferrite–PVDF composite materials. This study has helped us to understand the importance of magnetic Co2U-type hexaferrite nanomaterials for the fabrication of lightweight, large area, flexible, and thickness-controlled radar absorbing materials to combat against electromagnetic pollution. [ABSTRACT FROM AUTHOR]

A grand canonical multiscale space-charge model has been developed to study and predict the electrical properties of polycrystalline perovskites with complex defect chemistries. This model combines accurate data from hybrid exchange-correlation functional density functional theory calculations (defect formation energies, resultant grand canonical calculations of defect concentrations, and ionization states) with finite-element simulation of the electric field and its coupling to defect redistribution and reionization throughout the grain. This model was used to simulate the evolution of the oxygen partial pressure-dependent conductivity of polycrystalline acceptor-doped strontium titanate as the grain size decreases, and the results were compared to previous experiments. These results demonstrate that as the grain size is reduced from the microscale to nanoscale, the experimentally observed disappearance of ionic conductivity and forward shift of the oxygen partial pressure of the n–p crossover are successfully reproduced and explained by the model. Mechanistically, the changes to conductivity stem from the charge transfer from the grain boundary core into the grain interior, forming a space-charge layer near the grain boundary core that perturbs the local defect chemistry. The impact of the grain size on the electrical conductivity and the underlying defect chemistry across the grain are discussed. In addition to the findings herein, the model itself enables exploration of the electrical response of polycrystalline semiconductor systems with complex defect chemistries, which is critical to the design of future electronic components. [ABSTRACT FROM AUTHOR]

Studies on thermal and transport properties of topologically interesting polycrystalline ZrTe5 down to 2 K and magnetic fields up to 14 T are reported here. Attempts have been made to explain the metal insulator transition-like features seen in magnetic fields, a behavior characteristic of ZrTe5. The maximum in relative magnetoresistance (MRmax) for a particular magnetic field with respect to the peak temperature, i.e., Tp(B), shows an activated behavior reminiscent of polaronic conduction seen upon chemical substitution like Hf in Zr. Magnetoresistance is well described by a small polaron hopping transport model in a systematic way for various fields. The estimated activation energies are in line with infrared spectroscopy as well as hole dominated thermopower supported by heat capacity measurements. The essential features of the analysis include square root dependence of magnetoresistance with the magnetic field possibly due to the weak antilocalization effect as well as T3/2 dependence on mobility, extracted from a simplified two-band model fit in magnetoresistance curves. [ABSTRACT FROM AUTHOR]

Shearing of a solidified polycrystalline lubricant film confined between two solid surfaces has been studied by molecular dynamics simulations. In the case of a perfect commensurate contact, we observe interlayer slips within the film and shear-induced order-to-disorder transition of lubricant molecules around grain boundaries. This process is accompanied by the nucleation, propagation, and annihilation of dislocations in the solidified film, resulting in repeated dilation and collapse of the lubricant film during the stick–slip motion. In the case of an incommensurate contact, only slips at the lubricant–solid interface happen and no dilation of the lubricant film is observed during the stick–slip friction. These observations are consistent with recent surface force balance experimental measurements. In combination with our recent work [R. G. Xu and Y. S. Leng, Proc. Natl. Acad. Sci. U. S. A. 115, 6560 (2018)], this study provides a renewed picture on the physical property of nanoconfined lubricant films in boundary lubrication. [ABSTRACT FROM AUTHOR]

The spin Seebeck effect (SSE) is an emergent thermoelectric phenomenon, which enables a thermal-to-electrical energy conversion via the thermal injection of spin currents from a ferromagnet (FM) into an attached paramagnetic metal (PM). Recent studies have revealed that the SSE is very sensitive to the PM/FM interface condition, suggesting a potential way to enhance the SSE by controlling the interface condition. However, most of the previous studies are limited to conventional Pt/bulk single-crystal or thin-film YIG systems, lacking consideration for mesoscale surface defects such as pores and grain grooves, which frequently exist in more prevalent bulk polycrystalline magnets. Here, we investigate the effect of interface condition on the longitudinal SSE (LSSE) in a Pt/polycrystalline NiFe2O4 (NFO) slab system. Different interface conditions are induced by treating the surface of NFO slabs with varying combinations of polishing force (Fp) and post-annealing temperature (Ta) before the Pt deposition. The resultant LSSE signals show strong correlations with different interface parameters. In particular, we find that mesoscale surface defects (cracks, pores, and grain grooves) and the surface roughness play a crucial role in determining the magnitude of LSSE signals and demonstrate that those parameters can be deliberately controlled by properly choosing Fp and Ta. We report one sample with a spin Seebeck coefficient of 0.58 μV/K, which is significantly larger than that of bulk polycrystalline magnets reported thus far. [ABSTRACT FROM AUTHOR]

The linear magnetoresistance (LMR) effect is an interesting topic due to its potential practical applications in magnetoelectronic sensors and magnetic random-access memories. We report the LMR in polycrystalline Bi thin films synthesized by the molecular beam epitaxy method. Though the present films are complex and disordered, semimetal to semiconductor transition is observed due to the quantum size effect. The LMR of the topologically protected surface state dominated two-dimensional transport can be mainly described by the theory of mobility fluctuation based on the Parish-Littlewood (PL) model. In addition, when the temperature is below 10 K, the LMR is originated from the linear energy dispersion based on the quantum model as the supplement of the PL model. The combination of the quantum and PL model may shed light on the LMR essence of polycrystalline Bi films. [ABSTRACT FROM AUTHOR]

Here, we report on the dielectric and magnetic properties of polycrystalline samples of YMnO3 where the ratio between both orthorhombic (o-YMO) and hexagonal (h-YMO) phases has been controlled by means of appropriate sintering treatments. Interestingly, we observe that the dielectric behavior is dominated by the presence of the metastable o-YMO phase, even though its amount remains as a minority phase. However it also influences the magnetic behavior for sintering temperatures below 1000 °C, and in addition, a weak ferromagnetic contribution is always detected in our polycrystalline samples regardless of the o-YMO content. [ABSTRACT FROM AUTHOR]

When the stoichiometric proportion of Cu in Ca4 − xCuxTi4O12 polycrystalline ceramics is decreased from 3 to 2 and then to 1, the room-temperature permittivity is reduced by one order of magnitude during each step. Ca/Cu atomic disorder is observed only in some grains of Ca3CuTi4O12 single-phase polycrystalline ceramics, and the disorder is not the origin of the giant permittivity in CaCu3Ti4O12. Quantitatively, the permittivity magnitude is related to the mole ratio of polaronlike 3d electrons from Cu ions. [ABSTRACT FROM AUTHOR]

The calculation of space charge potential, the difference of the activation energy of grain boundary and grain, and the ratio of conductivity of grain boundary and grain at different temperatures of the polycrystalline ceramics have been reappraised in the present model, in which charge carriers hopping through bulk and grain boundary barriers with different mobility are taken into account. It is evidenced that the present model is valid and more precise than previous models, and thus, it is concluded that the assumption that the mobility of charge carriers hopping through bulk and grain boundary barrier is the same made by the previous studies is unsuitable. [ABSTRACT FROM AUTHOR]

Inorganic ferroelectrics have long dominated research and applications, taking advantage of high piezoelectric performance in bulk polycrystalline ceramic forms. Molecular ferroelectrics have attracted growing interest because of their environmental friendliness, easy processing, lightweight, and good biocompatibility, while realizing the considerable piezoelectricity in their bulk polycrystalline forms remains a great challenge. Herein, for the first time, through ring enlargement, a molecular ferroelectric 1‐azabicyclo[3.2.1]octonium perrhenate ([3.2.1‐abco]ReO4) with a large piezoelectric coefficient d33 up to 118 pC/N in the polycrystalline pellet form is designed, which is higher than that of the parent 1‐azabicyclo[2.2.1]heptanium perrhenate ([2.2.1–abch]ReO4, 90 pC/N) and those of most molecular ferroelectrics in polycrystalline or even single crystal forms. The ring enlargement reduces the molecular strain for easier molecular deformation, which contributes to the higher piezoelectric response in [3.2.1‐abco]ReO4. This work opens up a new avenue for exploring high piezoelectric polycrystalline molecular ferroelectrics with great potential in piezoelectric applications. [ABSTRACT FROM AUTHOR]

The reported experimental data of the temperature dependence of the electrical conductivity, σ(T), the Seebeck coefficient, S(T), and the Hall coefficient, RH(T) on n-type PdxCu1−xFeS2 (x = 0, 0.005, 0.01, and 0.02) polycrystalline samples have been analyzed including not only free-electron conduction in the 1st and the 2nd conduction band minimum (CBM) but also hopping conduction in an impurity band. The hopping mechanisms have been identified through the analysis of the reduced local activation energy of the conductivity. The amphoteric nature of Pd impurity atoms is assumed: a part of the doped Pd atoms are assumed to substitute the Cu-sites to form single donor states PdCu, while the rest are assumed to substitute the Fe-sites to form compensating acceptor states PdFe. Treating the density-of-states effective mass of the 1st CBM and the static dielectric constant as common fitting parameters, simultaneous fits to the σ(T), S(T), and RH(T) data have been successfully performed. Through the fits, the concentrations of donors and acceptors together with the ionization energies of the donor levels have been deduced for each sample. It is revealed that the concentration ratio of PdCu:PdFe is about 1.5:1. [ABSTRACT FROM AUTHOR]

The polycrystalline powder of CoMnP2O7 has been prepared via the conventional solid-state reaction route. The X-ray diffraction analysis revealed the formation of a single-phase monoclinic lattice system. The atomic positions as well as the characteristic interatomic distances and angles have been deduced through the Rietveld refinement. The SEM images indicate the polycrystalline nature of the material with grain size anisotropy. The CoMnP2O7 is identified as a wide direct band-gap material, further highlighting its potential use across a range of industries, including electronic and optical device manufacturing. Dielectric measurements have been performed in the temperature range of 298–800 K at different frequencies, and versus frequency under various temperatures. This material demonstrates promising characteristics for potential capacitor applications, as evidenced by its high dielectric constant and low losses. The CoMnP2O7 pyrophosphate presents high permittivity at low frequencies owing to Maxwell–Wagner polarization arising from the inter-grain boundaries, as confirmed through impedance spectroscopy. An equivalent circuit has been provided to model the electrical response. The ac-conductivity increases as the temperature increases, and oxygen vacancies dominate at high temperatures. The obtained results also suggest the possibility of using this material for capacitors as well as both NTC and PTC thermistors. [ABSTRACT FROM AUTHOR]

The structural, microstructural, dielectric, and conductivity properties of Tin modified Sodium Bismuth Titanate (Na 0.5 Bi 0.5)(Ti 1-x Sn x)O 3 , where x (mol%) = 0%, 1%, 3% (labeled as NBT, NBTS1, and NBTS3, respectively) were experimentally investigated in this paper. In this regard, the solid-state reaction process was used to prepare polycrystalline materials, where sintering was performed at 1100 °C for 3 h under atmospheric air. As a result, X-ray diffraction confirms, as it seems, the presence of a rhombohedral phase (R3c) in all compositions at room temperature. The electrical properties of the compositions are also studied using complex impedance spectroscopy (CIS). Subsequently, at room-temperature, doping 1% of Sn4+ in the NBT perovskite reduces the dielectric loss from 4.4 × 10−2 to 3.43 × 10−2 at 1 MHz. Moreover, it is around 3.05 × 10−2 at 93.6 °C and 1 MHz for NBTS3. Sn4+ significantly doping improved electrical conductivity. Therefore, at 10 Hz and 450 °C, the electrical conductivity of NBTS3 (σ ac = 8.76 × 10−3 S.m−1) is 61.26 times that of pure NBT (σ ac = 1.43 × 10−4 S.m−1). Joncher's power law investigates the conduction mechanism's nature; (i) the decreasing variation of the exponent s 1 with temperature suggests that the NBT compound is characterized by the CBH (Correlated Barrier Hopping) model. On the other hand, for NBTS1 and NBTS3 (ii), the increase in s 1 and s 2 parameters under temperature indicates that the NSPT (non-overlapping small polaron tunneling) model is the most dominant. In this work, all tested compounds exhibit a sort of ferroelectric relaxation behavior. Our results demonstrate that doped materials can be applied to solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films' structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu3N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm−1 range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu3N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu3N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu3N-based materials for efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

For the first time, using optical, scanning, and transmission electron microscopy and X-ray phase analysis in combination with measurements of tensile mechanical properties, we obtained data on the structural features of the polycrystalline shape-memory eutectoid Cu-Al-Ni-(B) alloys doped by aluminum (of 10 and 14 wt% Al in total amount), nickel (of 3, 4, and 4.5 wt% Ni), and boron (0.02–0.3 wt% B) in various compositions. The effect of boron on the grain sizes, structure, phase composition, and mechanical properties of shape memory (SM) alloys has been studied. The localization of aluminum borides in the structure was investigated and an effect of grain growth inhibition in the (α + β) and β Cu-Al-Ni-B alloys was established, both in the cast state of the alloys considered and after their heat treatment. [ABSTRACT FROM AUTHOR]

Proper analysis of vibrational sum-frequency generation (VSFG) spectra requires that the nonresonant contribution be dealt with correctly. This work shows that the temporal profile of the nonresonant SFG response varies with crystal facing and sample orientation for single-crystal Si and is significantly different than what is observed with polycrystalline Au. These considerations will affect the use of time-delay methods to experimentally suppress the nonresonant signal in broadband SFG measurements. Time-resolved or phase-sensitive SFG measurements will also need to properly account for these effects in post-processing. Graphical Abstract [ABSTRACT FROM AUTHOR]

We have investigated the grain-boundary scattering effect on the thermal transport behavior of uranium dioxide ( UO 2). The polycrystalline samples having different grain-sizes (0.125, 1.8, and 7.2 μ m) have been prepared by a spark plasma sintering technique and characterized by x-ray powder diffraction, scanning electron microscope, and Raman spectroscopy. The thermal transport properties (the thermal conductivity and thermoelectric power) have been measured in the temperature range of 2–300 K, and the results were analyzed in terms of various physical parameters contributing to thermal conductivity in these materials in relation to grain-size. We show that thermal conductivity decreases systematically with lowering grain-size in the temperatures below 30 K, where the boundary scattering dominates the thermal transport. At higher temperatures, more scattering processes are involved in the heat transport in these materials, making the analysis difficult. We determined the grain-boundary Kapitza resistance that would result in the observed increase in thermal conductivity with grain-size and compared the value with Kapitza resistances calculated for UO 2 using molecular dynamics from the literature. [ABSTRACT FROM AUTHOR]

This report is on the observation and theory for strong mechanical strain mediated magneto-electric (ME) coupling in composites of lead zirconate titanate (PZT) and self-biased Y- or W-type hexagonal ferrites. Polycrystalline Y-type (Ni1−xZnx)2 Y, and W-type (Co1−xZnx)2 W, hexagonal ferrites for x = 0–0.4 prepared by ceramic processing techniques showed a large remanent magnetization due to uniaxial or in-plane magneto-crystalline anisotropy. The strength of ME coupling in symmetric trilayer composites of the ferrites and PZT was measured by the ME voltage coefficient (MEVC) at low-frequencies and at longitudinal electromechanical resonance. The bias magnetic field H-dependence of MEVC at low-frequencies in the composites with (Ni, Zn) Y showed hysteresis with its value under self-bias 90% or more of the value for the optimum bias field. In the case of composites with W-type ferrites, the MEVC under zero-external bias was 60%–80% of its value for the optimum bias field. Both types of composites when subjected to an ac magnetic field at the EMR frequency showed an order of magnitude enhancement in the MEVC compared to low-frequencies and the peak value at EMR for zero-bias was 90% of its value under the optimum bias. A model has been developed for the large ME response under the self-bias provided by the remanent magnetization and estimated values of MEVC are in good agreement with the data. The hexaferrite-ferroelectric composites showing ME response without the need for an external magnetic bias are of importance for use as sensors and sensor arrays of magnetic fields. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of the effect of surface energy anisotropy on the tungsten surface relief modification under ion sputtering. In our experiments, the sputtering of textured polycrystalline tungsten with Ar ions resulted in a stepped surface relief formation. The surface after sputtering was analyzed using the electron backscatter diffraction and confocal laser scanning microscopy techniques. The formation of the stepped relief is explained by different surface energies of differently oriented grains (surface energy anisotropy). The surface energies of the three low-index W planes were calculated in the model of broken bonds. It is shown for the first time that the ratio of the sputtering depth of differently oriented grains of W is equal to the ratio of the differences of the surface energies of these grains. In that way, the ratio of the sputtering yields of differently oriented grains of tungsten can be quantified by knowing the surface energy, which depended on the reticular grain density and the number of broken bonds with nearest and next-nearest neighboring atoms on the surface using the broken bond model. It is shown that ion sputtering can be used as an instrument for studying the surface energy of solids. [ABSTRACT FROM AUTHOR]

We report the magnetoresistance study of an individual polycrystalline nickel nanowire at temperature T = 10 K. Transport measurements have indicated a large coercive field of the nanowire, justified by the polycrystalline structure of the studied sample, where both magnetocrystalline anisotropy of randomly oriented grains and effective uniaxial anisotropy at the grain boundaries enhance the coercive field. Magnetization reversal studied with micromagnetic simulations occurs via the curling mode when vortices are nucleated and propagate along the nanowire, and propagation is inhibited at grain boundaries. The applicability of micromagnetic simulations is confirmed by a good agreement between experimental and simulated magnetoresistance curves. [ABSTRACT FROM AUTHOR]

The spontaneous polarization in ferroelectrics provides an effective way to engineer interfacial charge distribution at the ferroelectric heterojunctions, thereby depletion width in p-n junction and energy band structures. Here, we integrated p-type multiferroic 7% neodymium-doped bismuth ferrite Bi 0.93 Nd 0.07 FeO 3 (BFO7Nd) polycrystalline ceramic bulk with n-type transparent conductive indium tin oxide (ITO) to demonstrate the influence of ferroelectric polarization on surface potential and its effect on photoelectrochemical (PEC) water reduction. Kelvin probe force microscopy (KPFM) results reveal the surface potential change during ferroelectric polarization switching, suggesting that the polarization bound charges may have an effect on space charge region between ITO-BFO7Nd, thus dominating surface potential at the electrode/electrolyte interface. This implies that the interface barrier between ITO and BFO7Nd can be easily modulated by polarization bound charges. The electron lifetime of upward-polarization (P-up) ITO-BFO7Nd is estimated 29.30 ms, about 15 times longer than unpoled ITO-BFO7Nd. The photocurrent density of P-up ITO-BFO7Nd is ∼1.2 × 10−6 A/cm2 (at 0 V vs RHE), which is one-order higher compared to that of the unpoled and P-down states under illumination with an intensity of 100 mWcm−2. This work shows that ferroelectric polarization combined with photogenerated carriers is an effective approach for effective charge transfer in multiferroic ceramic to boost PEC solar water splitting. [ABSTRACT FROM AUTHOR]

We use resistivity and current-voltage characteristics measurements to evaluate the impact of the disorder on the nature of the Berezinskii-Kosterlitz-Thouless transition in ultrathin niobium (Nb) films. The films, with thickness in the range of 3.6-8.5 nm, show the structural transition from polycrystalline to amorphous structure upon a decrease in the film thickness. We show that this transformation results in the smearing of the Berezinskii-Kosterlitz-Thouless transition, until eventually the Berezinskii-Kosterlitz-Thouless scenario breaks down due to film inhomogeneity. [ABSTRACT FROM AUTHOR]

Polycrystalline thin films of Bi2Te3, a well-known topological insulator (TI), grown by RF sputtering shows metallic-like transport for a wide range of temperatures, T = 50 K to T = 225 K. For T > 225 K, the sample shows activated transport.. The metallic-like behavior at low temperatures can be understood within a model of overlapping surface states of the TI nanocrystallites in the film, suggesting that TI thin films of polycrystalline nature may also stabilize topologically protected states. [ABSTRACT FROM AUTHOR]

Photovoltaic devices based on ferroelectric materials have broad application prospects; however, there are also problems of narrow bandwidth and low sensitivity. In this paper, polycrystalline BiFeO3 (BFO) films are prepared directly on n‐Si (100) substrates to form ferroelectric/semiconductor heterostructures, the electrical response of which under weak light intensity (0.8 W m−2) is systematically investigated. Accompanied by the dielectric relaxation originated from photocarriers, the polarization of BFO increases while the coercive voltage decreases. Especially, current–voltage (I–V) curve under negative bias voltage changes obviously with illumination, and cyclically switchable photocurrent is detected at 0 V bias, with the on‐off ratio increasing for lower temperature. Although the photoresponse is detectable in the broad wavelength range of 275–1100 nm, it is more pronounced for visible light. It is considered that the built‐in electric field of the PN junction at the BFO/n‐Si interface drives the separation and migration of photocarriers, which in turn affects the interface barrier and the distribution of monovalent oxygen vacancies (VO•$V_{\rm{O}}^ \bullet $) in BFO while producing the photovoltaic effect. This work provides an effective route for developing photodetectors with high sensitivity and broadband detection. [ABSTRACT FROM AUTHOR]

In this work, silver-doped La 0.85- x Sr 0.15 Ag x MnO 3 (LSAMO, 0.05 ≤ x ≤ 0.20) polycrystalline ceramics were prepared by the sol-gel method. The experimental characterization of ceramics revealed that Ag ions were bounded with the lattice matrix. The resistivity and the corresponding peak temperature coefficient (TCR) of LSAMO ceramics were systematically tuned by changing the Ag dopant content. Adjusting the proportion of Ag enabled one to vary the metal-insulator transition temperature (T MI) for LSAMO specimens in a wide range, and their peak resistivity temperature (T p) was increased from 299.6 to 335.7 K. At the same time, the peak TCR value achieved its maximum of 15.2% K−1 at the doping molar ratio x of 0.15 and the peak resistivity temperature (T k) of 294.1 K. In addition, the electrical transport was described in the context of the small polaron hopping (SPH) model and the phenomenological percolation model (PP) over the metal-insulator transition region. Under the combined action of the Jahn-Teller (JT) effect, the double exchange (DE) mechanism and the PP model, LSAMO ceramics possessing high TCR at room temperature were obtained by varying the amount of Ag doping. The observed properties suggest LSAMO material can be used in advanced uncooled infrared bolometers. [ABSTRACT FROM AUTHOR]

While progress has been made in the design of organic semiconductors (OSCs) with improved transport properties, the understanding of the mechanisms involved is still limited, hindering further development. In this study, the interplay between structural order and transport considering one single OSC, analogous to past research on silicon is investigated. Rubrene (C42H28) is selected as it spans transport mechanisms from thermally activated hopping in its amorphous form to band‐like in highly ordered crystals in the orthorhombic polymorph. Transport characterizations including variable temperature conductivity, advanced Hall effect, and magnetoresistance measurements are performed on rubrene films with varying levels of order (polycrystalline vs amorphous), crystal phase (orthorhombic vs triclinic), and morphologies (platelet‐like vs spherulitic grains). A conductivity tuning range over four orders of magnitude between polycrystalline (platelet‐like) orthorhombic and amorphous films is reported. As observed in silicon, transport in polycrystalline orthorhombic rubrene is limited by energy barriers at grain boundaries. Additionally, a gradual transition from predominantly band‐like to predominantly hopping transport with increasing disorder, reminiscent of observations in silicon is shown. Nevertheless, OSCs differ from covalently bonded silicon by their weak intermolecular interaction. This study highlights that molecular packing must be optimized in OSCs to favor advantageous π‐orbital overlap and optimized transport properties. [ABSTRACT FROM AUTHOR]