Narrow Hysteresis Research Articles

Kinetic origin of hysteresis and the strongly enhanced reversible barocaloric effect by regulating the atomic coordination environment

Hysteresis is an inherent property of first-order transition materials that poses challenges for solid-state refrigeration applications. Extensive research has been conducted, but the intrinsic origins of hysteresis remain poorly understood. Here, we report a study of the kinetic origin of hysteresis and the enhanced barocaloric effect (BCE) in MnCoGe-based alloys with ~2% nonmagnetic In atoms. First-principles calculations demonstrate that substituting In atoms at Ge sites rather than Co sites results in a lower energy barrier, indicating a narrower hysteresis for the former. Combining neutron powder diffraction (NPD) with magnetic and calorimetric measurements completely verified the theoretical prediction. Electron local function (ELF) calculations further reveal the atomic coordination origin of regulated hysteresis due to weaker Co–Ge bonds when In atoms replace Ge, which is opposite to Co sites. Moreover, we experimentally investigate the BCE and find that although MnCo(Ge0.98In0.02) has a lower barocaloric entropy change ΔSP than does Mn(Co0.98In0.02)Ge, the reversible ΔSrev of the former is advantageous owing to a smaller hysteresis. The maximum ΔSrev of MnCo(Ge0.98In0.02) is 1.7 times greater than that of Mn(Co0.98In0.02)Ge. These results reveal the atomic-scale mechanism regulating hysteresis and provide insights into tailoring the functional properties of novel caloric refrigeration materials.

Study of the properties and joint operation of resonant sound absorbers depending on their geometry and relative position

The research presented in the work focuses on a damper that utilizes an "intelligent" material called multilayer magnetorheological elastomer. These devices are of interest due to their ability to adjust the elastic properties, size, and shape of the working body by manipulating the external magnetic field. They also have a high load capacity. The effectiveness of the damper's vibration isolation is determined by its design, manufacturing technology, and the composition of the multilayer magnetorheological elastomer. The mechanical and magnetic hysteresis of the device allows for evaluating the controllability of the damper and its ability to absorb vibrations. Research results indicate the presence of a symmetric and narrow hysteresis loop, not exceeding 7 μm, within the operating range of control currents.

Spectroscopic Detection and Theoretical Description of Spin‐Crossover Effect in Co(II)‐terpyridine System

Spin‐crossover (SCO) effect on octahedral Co(II) centers is much rarer and less known than in the case of Fe(II) complexes, although it is no less promising for the development of fundamental research, sophisticated memories, and sensors. The representative compound [Co(terpy)2]I2·2H2O (terpy = 2,2′:6′,2′′‐terpyridine) was synthesized, and its physicochemical properties were studied both experimentally and theoretically. Magnetic experiments revealed a very gradual SCO between a low‐spin state (SCo(II)‐LS = 1/2) and a high‐spin state (SCo(II)‐HS = 3/2) for the pristine sample and an abrupt SCO with a narrow thermal hysteresis around 130 K for the desolvated sample. Moreover, temperature‐dependent vibrational and electronic spectroscopy were employed to track the evolution of spectroscopic features related to SCO and desolvation processes. Additionally, quantum chemical calculations were utilized to determine the electronic structure, molecular orbitals, and vibrations for different spin states at various temperatures, offering a more comprehensive understanding of the compound's spectroscopic and magnetic behaviors. These extensive investigations provide valuable insights into Co(II)‐based SCO materials and their theoretical underpinnings, paving the way for the application of their thermometric properties.

Modulation of solid solution in MgxMn1−xAl2xFe2(1−x)O4 spinel ceramics for multifunctional devices

AbstractSolid solution modulation is an ideal method for combining the advantages of different parent compounds while mitigating their disadvantages. Here, we investigated the thermal sensitivity, magnetic properties, and microwave absorption of MgxMn1−xAl2xFe2(1−x)O4 (0.2 ≤ x ≤ 0.8) spinel solid solution ceramics for application in multifunctional devices. The electrical transport and magnetic properties can be modulated by adjusting the solution ratio. The ceramics exhibit negative temperature coefficient characteristic. The B‐values from 5065–8056 K, suggesting accurate temperature measurements over a wide temperature range. As a type of soft magnetic material, it has a narrow hysteresis loop and high resistivity. Vector network analyzer studies indicate Mg0.2Mn0.8Al0.4Fe1.6O4 could be a candidate for microwave absorption in S‐band. This study successfully extends the applicability of MgxMn1−xAl2xFe2(1−x)O4 ceramics for high‐temperature thermistors and also confirms potential for multifunctional device.

Superelasticity with narrow stress hysteresis and high cyclic stability in Co–V–Al polycrystalline alloy

Superelasticity of shape memory alloy associated with the martensitic transformation is extremely attractive for applications in sensors and biomedical. This application requires narrow stress hysteresis to reduce energy dissipation and a stable superelasticity cycle is an important factor in their practical applications. Co–V–Al alloys have inimitable advantages due to their narrow stress hysteresis, low-cost, and corrosion resistance, but the low number of superelasticity cycles restricts its development. Here, we report an intrinsic Co58V29Al13 polycrystalline alloy with a superelasticity stress hysteresis of 30 MPa at room temperature, the lowest among the alloys in this system, and a superelasticity strain of 3.6%. In addition, the sample shows no significant decay trend after 500 loading and unloading cycles. The high number of superelasticity cycles is mainly due to the elastic stress field generated around the dislocation during the cycle, which provides internal stress for martensite nucleation and reduces energy dissipation during martensitic transformation. This work provides essential guiding significance for the design of high-performance superelasticity alloys.

Study of a damper based on a multilayer magnetorheological elastomer

The research presented in the work focuses on a damper that utilizes an "intelligent" material called multilayer magnetorheological elastomer. These devices are of interest due to their ability to adjust the elastic properties, size, and shape of the working body by manipulating the external magnetic field. They also have a high load capacity. The effectiveness of the damper's vibration isolation is determined by its design, manufacturing technology, and the composition of the multilayer magnetorheological elastomer. The mechanical and magnetic hysteresis of the device allows for evaluating the controllability of the damper and its ability to absorb vibrations. Research results indicate the presence of a symmetric and narrow hysteresis loop, not exceeding 7 μm, within the operating range of control currents.

Reversible reorientation of martensite variants in stress-induced martensite aged Co35Ni35Al30 single crystals

The paper reports the temperature dependence of the reversible reorientation of martensite variants during loading/unloading along the [001]B2||[001]L10-direction in compression in stress-induced martensite (SIM) aged at 423 K for 0.5 h under a compressive stress of 500 MPa applied along the [110]B2||[100]L10-direction Co35Ni35Al30 single crystals. A wide temperature range of reversible strain from 203 K to 413 K (210 K) is observed due to the stabilisation of the tetragonal L10-martensite variant V1 ([001]B2||[001]L10) during SIM-aging in these single crystals. The reversible strain in the range of 157 K (203 K<Tt<As=Af=360 K) is because of the reorientation of the L10-martensite variants V1-V2/V3. The superelasticity at Tt>Af=360 K occurred due to the stress-induced B2-L10(V2/V3) martensitic transformation (MT). Rubber-like behaviour develops in the range of 52 K (203 K<Tt<Mf*=255 K) and is characterised by a narrow stress hysteresis of 13 MPa and a reversible strain of −12.0 % due to the movement of the twinning boundaries (reversible twinning) in L10-martensite. The reversible strain reaches −10.2 % in the temperature range from Mf*=255 K to As=Af=360 K. This strain is associated with a new mechanism of L10-martensite variant reorientation, which occurs through a sequence of reverse and forward stress-induced L10(V1)-B2-L10(V2/V3) MTs and leads to the stages on the stress–strain curves. The reverse L10(V1)-B2 MT at loading and forward B2-L10(V1) MT at unloading on the first stage of the stress–strain curves are characterised by low critical stresses of 8–23 MPa, a narrow stress hysteresis of 3–19 MPa and a completely reversible strain of −6.0 %, which is stable for 100 loading/unloading cycles.

Li-doped transition metal high-entropy oxides (Li/TM-HEOs) as Li-Ion batteries cathodes: a first report on capacity fading and cycling stability

High-Entropy Oxides (HEOs) have gained significant attention for their wide range of compositions and potential applications across various sectors, including rechargeable batteries. This study explores the characterization of two distinct HEO systems as potential cathode materials for Lithium-ion batteries (LIBs). A series of rock salt structured HEOs with varying Li loadings (16Li/RS-HEO, 25Li/RS-HEO, 33Li/RS-HEO, and 41Li/RS-HEO) and a spinel-structured HEO with 16 mol% of Li loading (16Li/SP-HEO) were firstly synthesized through co-precipitation. Electrochemical analyses via cyclic voltammetry revealed stark differences in the behavior of these structures. The Li/SP-HEO sample displayed broad and strongly irreversible hysteresis cycles, while the Li/RS-HEO series manifested thin, narrow hysteresis cycles with single oxidation peaks between 0.5 V and 0.7 V. As the lithium content increases in the RS-HEO system, the cycling stability of the cell decreases, most likely due to the reduced ratio of transition metal cations to lithium ions. Although there was a noticeable decrease in capacity under higher current rates, the higher lithium loadings positively impact the cell capacity, albeit with notable capacity fading under higher current rates. Li-doped rock salt structured high entropy materials show potential for LIB cathodes in terms of high specific capacities; the observed stability issues at medium and high current densities indicate a rapid electrode degradation.

Dual Mode Optoelectronic Devices Based on 2D Single Crystalline VO2 Films with Controlled Metallic Domain Regime Induced Variable Hysteresis

AbstractThe multimode optoelectronic operation in a single component device is an attractive design strategy for future optoelectronics, which demands unique and complex multifunction. Here, a novel dual‐mode optoelectronic device with both memory and switching functionalities by utilizing alternating metallic stripe domain regime‐induced controllable hysteresis of two dimensional (2D)‐crystalline VO2 films is reported. It is found that the formation and disappearance of tensile strain‐induced metallic stripe domain arrays are susceptible to temperature‐induced thermal energy, allowing controllable hysteresis in electric field‐induced metal‐insulator transition (E‐MIT) by tuning the total region of aligned metallic stripe domains within the VO2 films through current flow‐induced thermal energy. Based on the tunable hysteresis in E‐MIT, the 2D‐crystalline VO2 film‐based device exhibits successful multimode optoelectronic memory and switching operations. The device with a large hysteresis width exhibits high‐performance optoelectronic memory behavior with a high on/off ratio of up to ≈55% and a long retention time over 5000 s response to a light pulse optically triggering MIT. On the other hand, the 2D‐crystalline VO2 film device with a narrow hysteresis width exhibits high performance of photodetection with a responsivity of 316 mA W−1 and response times of ≈1.2 and ≈2 µs at rise and fall, respectively.

Optical and ferroelectric properties of lead titanate nanocrystals dispersed within borate glass matrix

Lead titanate nanocrystals dispersed within the borate glass matrix (composite) with the composition 75 B2O3-25 PbTiO3 (in mol %) was prepared. The composite's XRD analysis indicated it contains glassy phase, and this was further confirmed by DSC study. TEM, SAED, and FTIR analyses provided evidence that the PbTiO3 nanocrystals dispersed within the borate glass matrix, establishing the composite nature of this sample. The average particle size found of PbTiO3 was determined to be 57.2 nm via TEM. The composite's FTIR analysis indicated the presence of BO3 with NBO's, and BO4 units. Additionally, the presence of the Ti3+ ions in TiO6 units as well as Ti4+ ions in TiO4 and TiO6 units. The Curie temperature (Tc) of PbTiO3 in present composite sample was confirmed through both DSC and dielectric studies. Optical analysis of this composite sample unveiled three transmission bands, one corresponding to the 3Γ5 →2Γ3 charge transfer transition between Ti3+ and Ti4+ions. While the other transitions 2B2g →2B1g and 2B2g →2A1g are corresponding to the octahedral of Ti3+ (3d1) ions in tetragonal distorted sites. The polarization-field (P-E) loops of this composite sample at various electric fields unveiled relatively narrow hysteresis loops.

High yield stress and narrow phase transformation hysteresis of thermomechanical-processing NiTiCu shape memory alloy

NiTiCu shape memory alloy is subjected to thermomechanical processing which deals with local canning compression followed by annealing at 300, 450 and 600 °C, respectively. Transformation temperatures of annealed NiTiCu specimens increase with elevating annealing temperature. Following annealing at 300 °C, NiTiCu specimen exhibits high yield stress of about 2000 MPa due to the existence of nanocrystalline grains. NiTiCu sample annealed at 600 °C possesses an extremely narrow phase transformation hysteresis width of about 1 °C. Nanotwins are found in NiTiCu sample annealed at 300 °C, while a large number of twin variants appear in NiTiCu samples annealed at 450 and 600 °C. Nanocrystalline grains contribute to suppressing the occurrence of twin variants. Furthermore, nanocrystalline grains are not beneficial to the formation of martensite variants. In the case of compressive loading, martensite reorientation and detwinning take place more readily in NiTiCu samples annealed at 450 and 600 °C.

TMD material investigation for a low hysteresis vdW NCFET logic transistor

Boltzmann limit is inevitable in conventional MOSFETs, which prevent them to be used for low-power applications. Research in device physics can address this problem by selection of proper materials satisfying our requirements. Recently, 2D transition metal di-chalcogenide (TMD) materials are gaining interest because they help alleviate short-channel effects and DIBL problems. The TMD materials are composed by covalently bonded weak van der Waals (vdW) interaction and can be realized as hetero structures with 2D ferro-electric material CuInP2S6 at the gate stack. This paper demonstrates a vdW negative capacitance field effect transistor (NCFET) structure in TCAD and the design was validated for voltage-current Characteristics. Parametric analysis shows MoS2 with phenomenal on/off ratio, narrow hysteresis than the counterparts. Simulation shows that MoS2 vdW NCFET has a high transconductance of 2.36 µS µm−1. A steep slope of 28.54 mV dec−1 is seen in MoS2 vdW NCFET which promises the performance of logic applications at a reduced supply voltage.

Microheater Topology for Advanced Gas Sensor Applications with Carbyne-Enriched Nanomaterials

The response characteristics of carbyne-enriched surface-acoustic-wave (SAW)-based gas sensors utilizing meander and rectangular microheater topologies were investigated to assess their desorption and recovery properties. Comparative analysis of contact resistance and interface capacitance before and after heating revealed minimal deviation in contact resistance, signifying strong thermal stability in the carbyne-enriched layer. However, the interface capacitance varied with the microheater size. Our analysis reveals that a small meander microheater configuration (line width: 300 µm) facilitates efficient sensor recovery at ethanol concentration measurements in the range of 180–680 ppm, maintaining a low deviation in time delay across different concentrations (~2.3%), resulting in a narrow hysteresis and linear sensor response. Conversely, the large meander microheater (line width: 450 µm) and rectangular dense microheater induce irreversible changes in the sensing structure, leading to a widened hysteresis at higher concentrations and increased power consumption. Recovery patterns display substantial deviations from initial values at different concentration levels. Higher concentrations exhibit broader hysteresis, while lower concentrations show narrower hysteresis loops, compared to the small meander microheater. The study offers insights into desorption rates, power consumption variations, and recovery behaviors related to different microheater configurations. It demonstrates the importance of microheater topology selection in tailoring recovery properties and response characteristics, contributing to the advancement of carbyne-based sensor technology.

Room-temperature elastocaloric effect in Co49Ni21Ga30 shape memory wires

We demonstrate appreciable room-temperature elastocaloric effect in the Co49Ni21Ga30 microwires prepared using the Taylor-Ulitovsky method. By forming an almost excellent [001]B2-oriented single crystal along the wire axis, extraordinary superelasticity with low critical stress and narrow stress hysteresis was achieved. Moreover, the wire exhibits room-temperature elastocaloric effect (ΔTad = −4.1 K) with no apparent degradation for 100 cycles. Due to its easy fabrication and the small scale, the wire is of great potential for advanced applications in miniature intelligent devices requiring refrigeration. This work also paves the way for developing other high-performance shape memory wires.

Transformation behavior and inverse magnetocaloric effect in Ni45Co5Mn36.7In13.3-xGex melt-spun ribbons

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni45Co5Mn36.7In13.3-xGex (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ0H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ0H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form.

Graphene oxide boosted high surface area CeO2 for humidity sensing

Precise measurement of humidity is of high significance in diverse fields like instrumentation, automated systems, agriculture and climatology. Herein as a first ever attempt, we report ceria-graphene oxide (CeO2-GO) composites as resistive type humidity sensor, that shows attractive response to moisture. High surface area ceria is synthesised via ammonia mediated precipitation from salt precursor, and CeO2-GO composites are achieved via hydrothermal route. The composites are well characterized using various analytical tools. Experiments using different mass ratios of GO in the composite show that there is an optimum amount of GO to realise maximum efficiency in the test parameters. It is further noted that the performance of the sensor is controlled by the active adsorption sites, which is proportional to surface area of the composite. An optimized CeO2-GO matrix yielded a response and recovery time of 19 s and 10 s respectively. The narrow hysteresis in moisture adsorption-desorption study and excellent stability for about 60 days are also observed for the system, warranting the successful utility of the system for practical applications.

Activating a high-spin iron(II) complex to thermal spin-crossover with an inert non-isomorphous molecular dopant.

[Fe(bpp)2][ClO4]2 (bpp = 2,6-bis{pyrazol-1-yl}pyridine; monoclinic, C2/c) is high-spin between 5-300 K, and crystallises with a highly distorted molecular geometry that lies along the octahedral-trigonal prismatic distortion pathway. In contrast, [Ni(bpp)2][ClO4]2 (monoclinic, P21) adopts a more regular, near-octahedral coordination geometry. Gas phase DFT minimisations (ω-B97X-D/6-311G**) of [M(bpp)2]2+ complexes show the energy penalty associated with that coordination geometry distortion runs as M2+ = Fe2+ (HS) ≈ Mn2+ (HS) < Zn2+ ≈ Co2+ (HS) ≲ Cu2+ ≪ Ni2+ ≪ Ru2+ (LS; HS = high-spin, LS = low-spin). Slowly crystallised solid solutions [FexNi1-x(bpp)2][ClO4]2 with x = 0.53 (1a) and 0.74 (2a) adopt the P21 lattice, while x = 0.87 (3a) and 0.94 (4a) are mixed-phase materials with the high-spin C2/c phase as the major component. These materials exhibit thermal spin-transitions at T½ = 250 ± 1 K which occurs gradually in 1a, and abruptly and with narrow thermal hysteresis in 2a-4a. The transition proceeds to 100% completeness in 1a and 2a; that is, the 26% Ni doping in 2a is enough to convert high-spin [Fe(bpp)2][ClO4]2 into a cooperative, fully SCO-active material. These results were confirmed crystallographically for 1a and 2a, which revealed similarities and differences between these materials and the previously published [FexNi1-x(bpp)2][BF4]2 series. Rapidly precipitated powders with the same compositions (1b-4b) mostly resemble 1a-4a, except that 2b is a mixed-phase material; 2b-4b also contain a fraction of amorphous solid in addition to the two crystal phases. The largest iron fraction that can be accommodated by the P21 phase in this system is 0.7 ± 0.1.

Room temperature spin crossover properties in a series of mixed-anion Fe(NH2trz)3(BF4)2-x(SiF6)x/2 complexes.

A series of mixed-anion Fe(NH2trz)3(BF4)2-x(SiF6)x/2 spin crossover complexes is obtained modifying the reaction time but also using an increase amount of tetraethyl orthosilicate as the source for the production and the incorporation of SiF62- competing with the BF42- anions present in the mother solution. The increase of the SiF62- anion inclusion to the detriment of the BF4- counterpart induces a shift of the temperature transition toward high temperatures leading to interesting bistability properties around room temperature with T1/2 spanning from 300 K to 325 K. Moreover, the implementation of a solid-liquid post synthetic modification approach from the Fe(NH2trz)3(BF4)2 parent complex with identical TEOS proportions and under certain experimental conditions lead systematically to the same Fe(NH2trz)3(BF4)1.2(SiF6)0.4 composition. This compound presents an abrupt spin crossover behaviour with a narrow hysteresis loop just above room temperature (320 K), which is stable under thermal cycling and along time with no specific storage conditions. Such crystalline powder sample incorporates homogeneous rod-shaped particles whose formation and physical properties can be followed simultaneously using infra-red spectroscopy, dynamic light scattering (DLS), transmission electronic microscopy (TEM) and optical reflectance. The observation of a stabilized single ca. 800 nm population of mixed-anion particles starting from insoluble various sizes (from nano- to microscale) Fe(NH2trz)3(BF4)2 particles supports the key role of the solvent (water molecules) on the separation, the reactivity and the reorganization of the 1D iron-triazole chains forming the packing of the structure.

(Invited) Thermally Oxidized Yttrium Oxide on Germanium for n-Mos Capacitor and Field-Effect Transistor

Germanium (Ge) has many exciting material characteristics, such as high carrier mobility and narrow bandgap in the near-infrared range. Thus it is suitable for various applications. A high-quality insulating film on Ge is required to apply Ge to novel electronic devices successfully. It is well known that GeO2 on Ge has good electrical characteristics as a gate insulator or interlayer (IL), similar to SiO2 on Si [1]. Unlike SiO2, however, GeO2 is thermodynamically unstable under atmospheric pressure at typical oxidation temperatures (~400 °C) and volatilizes as GeO [2,3]. Several methods have been developed to suppress GeO volatilization from the surface. For example, transition metals such as yttrium (Y) have been introduced into GeO2. Yttrium (Y)-doped GeO2 has excellent thermal, chemical, and electrical characteristics. In the capacitance–voltage measurement, it shows a low interface state density (D it) and a narrow hysteresis corresponding to the border trap (BT) density (N bt) of gate insulators [4]. Based on the above studies, we focused on metal Y deposition with subsequent thermal oxidation as an efficient alternative method to deposit Y-oxide as a gate insulator on Ge. This method has been studied to deposit Y2O3 as a gate insulator on Si [5]. Moreover, metal oxidation has been used to form various gate insulators on Ge, such as Al [6] and Hf [7]. In this study, we expect a capping layer of Y and oxidized Y to suppress GeO volatilization and stabilize the interface. We fabricated and evaluated metal-oxide-semiconductor (MOS) capacitors and MOS field-effect transistors (FETs) with either a thermally oxidized Y or a thermally oxidized Ge oxide layer. The structural analysis found that the insulator was divided into three layers: Y2O3, YGeO3, and GeOx from the top. The oxidation temperature affected only the thickness of the bottom GeOx layer. We found that the Y-oxide gate stack had better electrical characteristics and a lower D it and N bt than the thermally oxidized GeOx insulator. In contrast, the D it–energy distribution and N bt temperature dependence of the Y-oxide gate insulator were similar to those of the GeOx gate insulator. We examined these observations, including the structural analysis results. We found that thermally oxidized Y had a distinct advantage over thermally oxidized Ge oxide: the possibility of controlling the structure and electrical characteristics of the Ge gate stack, such as the GeOx thickness and the BT signal origin.[1] H. Matsubara et al., Appl. Phys. Lett. 93 (2008) 032104. https://doi.org/10.1063/1.2959731[2] S. K. Wang et al., J. Appl. Phys. 108 (2010) 054104. https://doi.org/10.1063/1.3475990[3] S. K. Sahari et al., J. Phys. Conf. Ser. 417 (2013) 012014. https://doi.org/10.1088/1742-6596/417/1/012014[4] C. Lu et al., J. Appl. Phys. 116 (2014) 174103. https://doi.org/10.1063/1.4901205[5] M. Gurvitch et al., Appl. Phys. Lett. 51 (1987) 919. https://doi.org/10.1063/1.98801[6] T. Ohno, et al., Appl. Phys. Lett. 107 (2015) 133107. https://doi.org/10.1063/1.4932385[7] T. Hosoi et al., Microelectron. Eng. 109 (2013) 137. https://doi.org/10.1016/j.mee.2013.03.115[8] W.-C. Wen et al., Mat. Sci. Semicond. Processing, accepted (2023).

Ferroelectric relaxor behaviour in Bi and K/Na-substituted solid solutions of tetragonal tungsten bronze PbNb2O6

Lead metaniobate (PbNb2O6 or PNO) belongs to the tetragonal tungsten bronze (TTB) family. There are three polymorphic forms of PNO: tetragonal (stable at high temperature), rhombohedral (stable at room temperature), and the metastable orthorhombic phase, which has ferroelectric properties. The metastable orthorhombic phase is formed by quenching from the high temperature tetragonal phase due to the reconstructive/sluggish tetragonal to rhombohedral phase transition. A suitable ionic substitution can also lead to the stable ferroelectric orthorhombic phase. Stabilization of the ferroelectric orthorhombic phase by ionic substitution, and the formation of ferroelectric relaxors with increased amounts of dopants is hereby reported for the compositions Pb(1-x)Bi(x/2K(x/2)Nb2O6 and Pb(1-x)Bi(x/2)Na(x/2)Nb2O6. The solid solutions of PNO showed evidence of linked dielectric relaxation and ferroelectricity, validating the distinctive ferroelectric relaxor behaviour for the compositions Pb0.6Bi0.2K0.2Nb2O6 and Pb0.6Bi0.2Na0.2Nb2O6. As the concentrations of bismuth (Bi) and potassium/sodium (K/Na) dopants increased, the Curie temperature (Tc), or the temperature corresponding to the maximum dielectric permittivity (Tm), dropped. By using the Uchino-Nomura relation as a modification of the Curie-Weiss law, it was established that the Pb0.6Bi0.2K0.2Nb2O6 solid solution exhibit higher degree of diffuseness than Pb0.6Bi0.2Na0.2Nb2O6 at the transitions. The width of the ferroelectric hysteresis loop increased as the percentage of dopants increased, from x = 0.1 to x = 0.3. At x = 0.4, a narrow ferroelectric hysteresis loop and a frequency-dependent Tm abruptly formed, which is indicative of a ferroelectric relaxor.