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A layered chalcogenide material, tin monoselenide (SnSe), has recently garnered considerable interest in optoelectronics owing to its remarkable opto-electrical properties. Our goal in conducting this research is to better understand the SnSe vast off-stoichiometry ratio. The structural properties of all films examined by X-ray diffraction (XRD) confirmed formation of orthorhombic SnSe with a prominent (111) orientation peak. Raman spectroscopy revealed the successful formation of a single phase of α-SnSe under Sn-rich conditions. The calculated direct bandgap using Tauc’s plot is found to be increased from 1.37 eV (under Sn rich) to 1.68 eV (under Se-rich). Based on Hall measurement, largest carrier mobility (34.3 cm2V−1S−1) is found in Sn-rich SnSe conditions. The results show how off-stoichiometry-related imperfections have a significant impact on optoelectrical characteristics. And by adjusting the Sn/Se ratio, the conductivity type can be modified. Using this approach will undoubtedly result in an improvement in the overall performance of thin-film solar cells. This will enable the fabrication of extremely efficient SnSe homojunction solar cells. [ABSTRACT FROM AUTHOR]

In the present work, CdSe thin film has been deposited on indium tin oxide (ITO)-coated glass substrate by the pulsed laser deposition (PLD) technique. Temperature-dependent current–voltage and capacitance–voltage characterization approaches are used to study the influence of post-deposition heat treatment (at temperatures of 150, 250, and 350 °C) on electrical properties. It is observed that the zero-bias barrier height and the ideality factor are substantially temperature dependent. The Mott–Schottky plot confirmed that the prepared CdSe thin film is an n-type semiconductor. The bandgap is estimated from the absorption data of the UV–Vis spectrometer using Tauc's plot. This paper provides a thorough explanation of how electronic energy level diagram of the CdSe thin film on ITO-coated glass substrate was determined. [ABSTRACT FROM AUTHOR]

Optical and structural properties of pulsed laser-deposited CdSSe thin films were grown using different temperatures on different substrates. The results of optical and structural investigation show that these films are suitable for optoelectronics applications. The energy band gap lies in the range that is suitable for the desired purpose. x-ray diffraction (XRD) analysis indicated preferential orientation in the (220) direction. The band gap energy of these films is in the range of 2.277 to 2.641 eV. [ABSTRACT FROM AUTHOR]

Solid acid composite electrolytes RbH2PO4/LaPO4 were prepared with the molar percentage ratio and observed the structural, thermal, and transport properties. The superprotonic phase transition was identified in RbH2PO4 at 250 °C. The outstanding performance of RbH2PO4 was enhanced due to the addition of LaPO4 in the form of conductivity and stability. An enhancement in conductivity of 3–5 orders of magnitude was found at high temperatures compared to low temperatures in composite electrolytes. Thermal characterization showed that by introducing the additives, the dehydration behavior in DSC at higher temperatures shifted to lower. The minimum weight loss of composite indicates stability with LaPO4. Stable protonic conductivity for RbH2PO4 and composites was observed in a hermetically closed chamber and also under highly humidified conditions. The ionic conductivity and thermal stability of RbH2PO4/LaPO4 is the key point of our study that lays the foundation for the study of the solid electrolytes composites mechanism. [ABSTRACT FROM AUTHOR]

In the present investigation, ZnO thin films were deposited on an ITO coated glass substrate using the Pulsed Laser Deposition technique at different annealing temperatures, from 150 to 300 °C. Investigation showed the post-annealing process affected the topological structure and optical properties of ZnO thin films, which were investigated by Atomic Force Microscopy (AFM), and UV–Vis spectroscopies respectively. Temperature-dependent Raman spectroscopy and X-ray Diffraction (XRD) were used to confirm the presence of ZnO material. Surface roughness was analyzed by the AFM technique which indicates that it is slightly affected by annealing temperature. Optical transmittance data showed high transmittance about ∼ 70% within the visible region. The direct energy bandgap, complex refractive index, the complex dielectric constant was calculated through transmittance and absorption data. The optical band gap was 3.143 eV, firstly dropped to 3.112 eV and then increased to 3.171 eV with increasing the annealing temperatures. The surface roughness of ZnO thin films was associated with variations in optical band gap, indicating that the post-growth annealing method has a substantial impact. [ABSTRACT FROM AUTHOR]

Solid acid composite electrolytes (1−x)CsH2PO4(CDP)/xSiO2 (0 ≤ x ≤ 0.35) were prepared and observed the structural, thermal, and transport properties by XRD, EDX, FESEM, FTIR, DSC, TGA, DTA, and conductivity measurements. The crystallite size was obtained between the range of 36 and 64 nm. We have investigated the superprotonic phase transition at 230 °C in CDP, at which the conductivity increased up to four orders of magnitude. The initial dehydration event in CDP occurred at 250 °C. The performance of CDP was increased due to the addition of SiO2 in the form of conductivity and stability. Thermal characterization showed that by introducing the additives, dehydration behavior shifted to the lower in DSC and DTA at the higher temperature. The lowest weight loss was found in 65CDP/35SiO2. The stable protonic conductivity was observed with time for CDP, 95CDP/05SiO2, and 85CDP/15SiO2 in a hermetically closed chamber. The electrodes were prepared by vapor deposition of silver. [ABSTRACT FROM AUTHOR]

Solid acid composite electrolytes CsH2PO4(CDP)/NaH2PO4(SDP)⋅2H2O were prepared and observed the structural, thermal and transport properties by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray analysis, differential scanning calorimetry, fourier transform infrared spectroscopy, and conductivity measurement. We have investigated superprotonic phase transition at 235°C in CDP, at which the conductivity increased up to 2 to 3 orders of magnitude. The initial dehydration event in CDP occurs at 250°C. The performance of CDP was increased due to the addition of SDP⋅2H2O in the form of stability. Thermal characterization showed that introducing the additivities, dehydration behavior shifted to the lower at the higher temperature. The conductivity is increased above the temperature of 170°C which was found of the composite electrolytes 70CDP/30SDP⋅2H2O, 60CDP/40SDP⋅2H2O. The electrodes were prepared by a vacuum coating unit of silver. [ABSTRACT FROM AUTHOR]

Increased magnetic properties of La and Gd substituted bismuth ferrite (Bi0.9La0.1Fe1-xGdxO3) (BLFGO) ceramics are reported. Considering perovskite structure of bismuth ferrite (BiFeO3), Bi and Fe sites were partially substituted by La and Gd, respectively. These materials were synthesized by conventional solid state reaction method. Crystal structure and phase purity were confirmed by X-ray diffraction and Raman scattering spectroscopy at room temperature. A considerable improved ferromagnetic properties with double remnant magnetization of 0.184 emu/g was observed by increasing Gd ratio up to 5%. With different ionic sizes and due to magnetic moment of Gd, an induced deformation of spin cycloid structure had thereby resulted in net magnetization. Also, we monitor some decrease in dielectric loss upon La and Gd substitutions. Additionally, these ceramics showed significant magnetoelectric coupling. Such improvements on magnetic, insulation, and magnetoelectric properties demonstrated the potential of BLFGO for possible multiferroic device applications. [ABSTRACT FROM AUTHOR]

In recent years, ferroelectric random access memory has drawn considerable attention as promising replacement to both dynamic random access memory and flash memory. Specifically in metal-ferroelectric-insulator-semiconductor (MFIS)-based structures, bi-stable polarization of ferroelectric gate even in absence of power holds the resistance state of semiconductor-drain channel between two logic states and offers additional features of non-destructive readout and non-volatile storage capability. However, insulating layer in such structure leads to high depolarizing field across FE layer and in turn high-voltage operation. In the present work, comprehensive performance of low-voltage-driven MFIS device, i.e., Pt (40 nm)/BiFeO (265 nm)/DyScO (6 nm)/Si is evaluated for gate voltage stress (± 2 to ± 9 V) at different thermal agitation (200-400 K). Fat capacitance-voltage ( C- V) hysteresis centered at zero bias with large memory window (Δ V ) of 1.9 V at low operating voltage of ± 5 V, and stable data retention with distinguishable ON/OFF state values specifies strong charge storage potential of MFIS device in extreme conditions of ± 100 K. X-ray diffraction revealed polycrystalline and rhombohedral R3c phase of BiFeO film and out-of-plane piezoresponse force microscopy analysis showed the ultrafast domain switching with sharp contrast. Complete 180° phase reversal in hysteresis loop and bufferfly-shaped piezo-actuation amplitude loop further confirmed the enhanced ferroelectric properties of BiFeO thin films. Nonlinear J- V curves of MFIS structure were investigated to understand the device reliability and charge transport mechanism. These encouraging results are crucial for designing more reliable integrated MFIS-based non-destructive readout non-volatile memory devices. [ABSTRACT FROM AUTHOR]

Highly oriented PbZr0.53Ti0.47O3/CoFe2O4 (PZT/CFO) multilayered nanostructures (MLNs) were grown on MgO substrate by pulsed laser ablation using La0.5Sr0.5CoO3 (LSCO) as conducting bottom electrode. The effect of various PZT/CFO (PC) sandwich configurations having three, five, and nine layers while maintaining total thickness of PZT and CFO be identical has been systematically investigated. X-ray diffraction (XRD) and micro-Raman spectra revealed the existence of pure PZT and CFO phases without any intermediate phase. Intact MLNs were observed by transmission electron microscopy (TEM) with little inter-diffusion near the interfaces at nano-metric scale without any impurity phase. Impedance spectroscopy, modulus spectroscopy, and conductivity spectroscopy were carry out over a wide range of temperatures (100–600 K) and frequencies (100 Hz–1 MHz) to investigate the grain and grain boundary effect on electrical properties of MLNs. Temperature dependent real dielectric permittivity and dielectric loss illustrated step-like behavior and relaxation peaks near the step-up characteristic, respectively. Cole–Cole plots indicate that most of the dielectric response came from the bulk (grain) MLNs below 300 K, whereas the grain boundary and the electrode–MLNs effects are prominent at elevated temperatures. The dielectric loss relaxation peak shifted to higher frequency side with increase in temperature, it was out of the experimental frequency window above 300 K. Our Cole–Cole fitting of dielectric loss spectra indicated marked deviation from the ideal Debye-type of relaxation, which is more at elevated temperature. Master modulus spectra supported the observation from the impedance spectra; it also indicated that the magnitude of the grain boundary compared to grain becomes more prominent with increase in number of layers. We have explained these electrical properties of MLNs by Maxwell–Wagner type contributions arising from the interfacial charge at the interface of the ML structures. Three different types of frequency dependent conduction processes were observed at elevated temperatures (>300 K), which fitted well with the double power law, $$ \sigma \left( \omega \right) = \sigma \left( 0 \right) + A_{1} \omega^{{n_{1} }} + A_{2} \omega^{{n_{2} }} , $$ indicating that the low frequency (<1 kHz) conductivity may be due to long-range ordering (frequency independent), mid frequency conductivity (<10 kHz) may be due to short-range hopping, and high frequency (<1 MHz) conduction due to the localized relaxation hopping mechanism. Ferroelectric polarization decreased slowly in reducing the temperature from 300 to 200 K, with complete collapse of polarization at ~100 K, but there was complete recovery of the polarization during heating, which was repeatable over many different experiments. At the same time, the temperature dependent remanent magnetization of the MLNs showed slow enhancement in the magnitude till 200 K with three-fold increase at 100 K compared to room temperature. This enhancement in remanent magnetization and decrease in remanent ferroelectric polarization on lowering the temperature indicate temperature dependent dynamic switching of ferroelectric polarization. The magnetic and ferroelectric properties of MLNs were quite different compared to individual layers suggesting its improper ferroelectric characteristics. The fatigue test showed almost 0–20% deterioration in polarization. Fatigue and strong temperature and frequency dependent magneto-electric coupling suggest MLNs utility for Dynamic Magneto-Electric Random Access Memory (DMERAM). [ABSTRACT FROM AUTHOR]

Downscaling limitations and limited write/erase cycles in conventional charge-storage based non-volatile memories stimulate the development of emerging memory devices having enhanced performance. Resistive random-access memory (RRAM) devices are recognized as the next-generation memory devices for employment in artificial intelligence and neuromorphic computing, due to their smallest cell size, high write/erase speed and endurance. Unipolar and bipolar resistive switching characteristics in graphene oxide (GO) have been extensively studied in recent years, whereas the study of non-polar and complementary switching is scarce. Here we fabricated GO-based RRAM devices with gold nanoparticles (Au Nps). Diverse types of switching behavior are observed by changing the processing methods and device geometry. Tri-layer GO-based devices illustrated non-polar resistive switching, which is a combination of unipolar and bipolar switching. Five-layer GO-based devices depicted complementary resistive switching having the lowest current values ~12 µA; and this structure is capable of resolving the sneak path issue. Both devices show good retention and endurance performance. Au Nps in tri-layer devices assisted the conducting path, whereas in five-layer devices, Au Nps layer worked as common electrodes between co-joined cells. These GO-based devices with Au Nps comprising different configuration are vital for practical applications of emerging non-volatile resistive memories. [ABSTRACT FROM AUTHOR]

We have studied the atomic force microscopy (AFM), X-ray Bragg reflections, X-ray absorption spectra (XAS) of the Pd L-edge, Scanning electron microscopey (SEM) and Raman spectra, and direct magnetoelectric tensor of Pd-substituted lead titanate and lead zirconate-titanate. A primary aim is to determine the percentage of Pd+4 and Pd+2 substitutional at the Ti-sites (we find that it is almost fully substitutional). The atomic force microscopy data uniquely reveal a surprise: both threefold vertical (polarized out-of-plane) and fourfold in-plane domain vertices. This is discussed in terms of the general rules for Voronoi patterns (Dirichlet tessellations) in two and three dimensions. At high pressures Raman soft modes are observed, as in pure lead titanate, and X-ray diffraction (XRD) indicates a nearly second-order displacive phase transition. However, two or three transitions are involved: First, there are anomalies in c/a ratio and Raman spectra at low pressures (P = 1 − 2 GPa); and second, the c/a ratio reaches unity at ca. P = 10 GPa, where a monoclinic (Mc) but metrically cubic transition occurs from the ambient tetragonal P4 mm structure in pure PbTiO3; whereas the Raman lines (forbidden in the cubic phase) remain until ca. 17 GPa, where a monoclinic-cubic transition is known in lead titanate. [ABSTRACT FROM AUTHOR]

We show the ability to map the phase diagram of a relaxor-ferroelectric system as a function of temperature and composition through local hysteresis curve acquisition, with the voltage spectroscopy data being used as a proxy for the (unknown) microscopic state or thermodynamic parameters of materials. Given the discrete nature of the measurement points, we use Gaussian processes to reconstruct hysteresis loops in temperature and voltage space, and compare the results with the raw data and bulk dielectric spectroscopy measurements. The results indicate that the surface transition temperature is similar for all but one composition with respect to the bulk. Through clustering algorithms, we recreate the main features of the bulk diagram, and provide statistical confidence estimates for the reconstructed phase transition temperatures. We validate the method by using Gaussian processes to predict hysteresis loops for a given temperature for a composition unseen by the algorithm, and compare with measurements. These techniques can be used to map phase diagrams from functional materials in an automated fashion, and provide a method for uncertainty quantification and model selection. Piezoelectrics: Seeing the full picture with machine learning The functional response of piezoelectrics for arbitrary compositions and conditions cannot be fully obtained using local probes. Although the ferroelectric to paraelectric phase transition temperature can be measured, this is only for a limited number of data points. Now, a team led by Rama Vasudevan at Oak Ridge National Laboratory and colleagues in Puerto Rico, the United States, and India demonstrate that machine learning can be used to obtain the full ferroelectric phase diagram, with functional response. From measurements on four samples of a material, they use a machine-learning technique called Gaussian processes to reconstruct piezoelectric properties for continuously varying voltages and temperatures, which with more commonly used approaches accurately predicts ferroelectric phase diagrams. This could be used to generate piezoelectric phase diagrams, highlighting material compositions with optimal properties that can then be targeted by synthesis. [ABSTRACT FROM AUTHOR]

Multiferroic materials have attracted considerable attention as possible candidates for a wide variety of future microelectronic and memory devices, although robust magnetoelectric (ME) coupling between electric and magnetic orders at room temperature still remains difficult to achieve. In order to obtain robust ME coupling at room temperature, we studied the Pb(Fe0.5Nb0.5)O3/Ni0.65Zn0.35Fe2O4/Pb(Fe0.5Nb0.5)O3 (PFN/NZFO/PFN) trilayer structure as a representative FE/FM/FE system. We report the ferroelectric, magnetic and ME properties of PFN/NZFO/PFN trilayer nanoscale heterostructure having dimensions 70/20/70 nm, at room temperature. The presence of only (00l) reflection of PFN and NZFO in the X-ray diffraction (XRD) patterns and electron diffraction patterns in Transmission Electron Microscopy (TEM) confirm the epitaxial growth of multilayer heterostructure. The distribution of the ferroelectric loop area in a wide area has been studied, suggesting that spatial variability of ferroelectric switching behavior is low, and film growth is of high quality. The ferroelectric and magnetic phase transitions of these heterostructures have been found at ~575 K and ~650 K, respectively which are well above room temperature. These nanostructures exhibit low loss tangent, large saturation polarization (Ps ~ 38 µC/cm2) and magnetization (Ms ~ 48 emu/cm3) with strong ME coupling at room temperature revealing them as potential candidates for nanoscale multifunctional and spintronics device applications. [ABSTRACT FROM AUTHOR]

We present detailed Raman studies of SrZrO3 (SZO) that show three anomalies in Raman modes: One has a small jump in frequency ω, one has its intensity vanish, and a third has a sharp change in temperature derivative dω(T)/dT from flat below T = 600 K to a Curie–Weiss dependence above 600 K with extrapolation to zero frequency at the known transition temperature T = 970 K, thereby proving the latter to be displacive. In addition, the P4mm ferroelectric phase predicted at high stresses has preliminary support from polarization-voltage experiments. The inference of a new transition in the temperature region 600–650 K is in disagreement with neutron studies. Comparisons are given for family member SrSnO3 and SrHfO3, and we discuss the different conclusions of Kennedy and Knight. We show that a known transition in SrHfO3 is also displacive with a well-behaved soft mode. Dielectrics: into a new phase An unexpected atomic arrangement in a material useful for electronics is identified by researchers in India, the UK, and the USA. Ashok Kumar from the CSIR-National Physical Laboratory and co-workers observe a phase change in strontium zirconate at 650 K. Strontium zirconate is an electrical insulator that has great potential in the semiconductor-technology because of its large dielectric constant. As this so-called perovskite is heated, its atomic structure changes at specific temperatures. But the sequence of these phase changes is still a matter of debate. Kumar and colleagues study the structure of strontium zirconate by measuring the optical emission associated with atomic vibrations—a method known as Raman spectroscopy and dielectric spectroscopy. They identify three anomalous features in these results that infer the presence of a new phase transition. [ABSTRACT FROM AUTHOR]