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Lead-free piezoelectric ceramics of (1 − x)K0.5Na0.5NbO3-xCaTiO3 were fabricated, and their crystal structure, microstructure, and electrical properties were systematically studied. Rietveld refinement of the x-ray diffraction data and Raman spectroscopic analyses revealed a composition-dependent structural phase transition: three phase transitions, namely, from a pure orthorhombic phase for x ≤ 0.02 to a mixed phase of orthorhombic and tetragonal phases (0.03 ≤ x ≤ 0.08) and finally another mixed phase of tetragonal + cubic for x = 0.10 and 0.15 at room temperature (RT). The morphological study reveals a decrease in grain size along with a more uniform distribution of grains as the concentration of CaTiO3 (CT) increases; notably, a homogeneous distribution of grains is observed for x = 0.05. The temperature-dependent dielectric properties show two phase transitions, from orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), for unmodified K0.5Na0.5NbO3 (KNN). However, both the phase transition temperatures (TO-T and TC) decrease, and the transition peaks broaden with an increase in CT substitution, and for x > 0.06, the TO-T shifted below RT. The broadening of the transition peak at TO-T may be due to the relaxation behavior. Among the prepared samples, the 5 mol. % CT-modified KNN shows the optimum electrical properties (d33 = 114 pC/N, ɛr = 412, and 2Pr = 15.25 μC/cm2) at RT. The enhanced electrical properties for x = 0.05 are due to the coexistence of orthorhombic and tetragonal phases, facilitating easy polarization rotation and flattening of the free energy profile. A phase diagram has been constructed based on the information gathered from the temperature-dependent dielectric measurements, RT x-ray diffraction, and Raman spectroscopy data and is discussed in detail. [ABSTRACT FROM AUTHOR]

The development of multi‐stimuli‐responsive (MSR) materials is a tempting yet intriguing challenge due to the absence of a defined design approach. In this study, we designed and synthesised two compounds based on triphenylamine, namely, TPA‐Tz1 and TPA‐Tz2. The photoluminescent investigations reveal the MSR behaviour of both compounds. TPA‐Tz1 shows reversible mechanochromism with a blue‐shifted emission due to changes in intermolecular interactions. Furthermore, both compounds exhibit solvatochromism in solvents of varying polarity. Detailed studies suggest that solvatochromism in TPA‐Tz1 can be attributed to twisted intramolecular charge transfer (TICT), while in TPA‐Tz2, it is due to intramolecular charge transfer (ICT). Additionally, both compounds display acidochromic properties in solution as well as in the solid state due to the protonation of the triazole ring. All changes in emissions are corroborated through theoretical calculations. The results provide insights into the intricate interplay of molecular interactions and structural rearrangements that contribute to the compound's multifaceted responsiveness. [ABSTRACT FROM AUTHOR]

BackgroundRecent HIV prevention trials required use of effective contraceptive methods to fulfill eligibility for enrollment. We compared pregnancy rates in a subset of participants enrolled in the Microbicide Trials Network protocol (MTN-003), a randomized trial of chemoprophylaxis to prevent HIV acquisition among women aged 18-45 years who initiated depot medroxyprogesterone acetate (DMPA) or combined oral contraceptives (COCs) at enrollment, relative to those already using DMPA or COCs.MethodsData were analyzed from MTN-003 participants from Uganda. Before enrollment, information on contraceptive type and initiation date was obtained. Urine pregnancy tests were performed at monthly follow-up visits. Cox proportional hazards models were used to compare pregnancy incidence among new users (initiated ≤60 days before enrollment) and established users (initiated >60 days before enrollment).ResultsOf 322 women enrolled, 296 were COC or DMPA users, 82 (28%) were new users, and 214 (72%) were established users. Pregnancy incidence was higher among new contraceptive users compared to established users (20.70% vs. 10.55%; adjusted hazard ratio [HR] = 1.66; 95% confidence interval [95% CI] 0.93-2.96). Among DMPA users, pregnancy incidence was 10.20% in new users versus 3.48% in established users (HR = 2.56; 95% CI 0.86-7.65). Among new COC users, pregnancy incidence was 42.67% in new users versus 23.67% in established COC users (adjusted HR = 1.74; 95% CI 0.87-3.48).ConclusionsNew contraceptive users, regardless of method, at the Uganda MTN-003 site had an increased pregnancy risk compared to established users, which may be due to contraceptive initiation primarily for trial eligibility. New users may benefit from intensive contraceptive counseling and additional contraceptive options, including longer acting reversible contraceptives.

This article provides a comprehensive report on the rhodium(III)-catalyzed C–H activation in indole from 2017 to 2022. The direct functionalization of C–H bonds offers a more sustainable and economically sensible route in organic synthesis, reducing the production of hazardous waste. Rhodium has been widely used as a catalyst for C–H functionalization due to its excellent functional group compatibility, versatility, reactivity, and selectivity. The article focuses on the utilization of Rh(III) catalyst for C–H activation of the indole moiety, which is a structurally important building block in natural products and pharmaceutical treatments. Various methods for directed C–H functionalization of indoles, such as C2 activation, alkylation, hydroarylation, and dual C–H activation reactions, are discussed. The text also discusses various methods for the synthesis of carbazole derivatives, benzo[e]indoles, and selective functionalization of indoles through C–H activation. While progress has been made in this area, there are still challenges to overcome, such as the need for harsh reaction conditions and stoichiometric metal oxidants. Continued research in this field is expected to improve reaction conditions and increase overall efficiency. [Extracted from the article]

Doping of suitable metal ions in ferroelectric oxides modifies the physical properties and can induce additional functionalities. Here, we present a detailed study on the effects of Sm concentration on the structural, dielectric, ferroelectric, and piezoelectric properties of ((K0.5Na0.5)1−3xSmx)NbO3 (KNSN) (0.00 ≤ x ≤ 0.02) ceramics. X‐ray diffraction and Raman spectroscopic analysis indicate that KNSN ceramics exhibit the single‐phase orthorhombic (Amm2) structure for x = 0.00 and the coexistence of orthorhombic and tetragonal (Amm2 + P4mm) structure for the composition range 0.005 ≤ x ≤ 0.02. The tetragonal phase fraction increases with an increase in Sm concentration. We observed dielectric relaxation behavior in KNSN at orthorhombic to tetragonal (TO–T) phase transition temperature, and its origin can be attributed to the structural heterogeneity at the inter‐ferroelectric phase boundary. Increasing Sm concentration leads to the broadening of the ferroelectric phase transition peaks. Further, the structural heterogeneity of the ceramics was seen from the slope of the dielectric constant versus log frequency and central peak behavior of Raman spectra at room temperature (RT). The study reveals that x = 0.005 shows maximum dielectric constant (Ɛr = 583), remanent polarization (2Pr = 57.02 μC/cm2), and piezoelectric coefficient (d33 = 94 pC/N) at RT and is associated with increased local structural heterogeneity due to Sm doping. [ABSTRACT FROM AUTHOR]

One of the important requirements for piezoelectric materials for use as high strain actuators is that they exhibit large unipolar electrostrain with minimum hysteresis. While large unipolar electrostrain >1% is generally achievable in good quality single crystals, most polycrystalline piezoelectric show low values < 0.4%. Unipolar electrostrain 0.5%–0.7% in polycrystalline piezoelectrics has often been reported in Na0.5Bi0.5TiO3-based compositions at the non-ergodic ergodic boundary. Not amenable to poling, such materials exhibit almost nearly zero direct piezoelectric coefficient (d33 ∼ 0 pC/N) and cannot be simultaneously used as a sensor. In this paper, we report a combination of large unipolar electrostrain of ∼0.6% with small strain hysteresis of 25% in a Sn-modified relaxor ferroelectric system PbTiO3–Bi(Ni1/2Zr1/2)O3. It exhibits d33 ∼ 340 pC/N, which is stable up to 130 °C, and large signal converse piezoelectric coefficient d33* ∼ 1200 pm/V. A combination of large d33 and d33* in the same material makes it an important candidate for simultaneous use as a sensor and high strain actuators. X-ray diffraction study in situ with the electric field suggests that large electrostrain with low strain hysteresis in this system is because of the increased reversible switching of the field stabilized tetragonal ferroelastic domains. [ABSTRACT FROM AUTHOR]

Ferroelectric materials exhibiting switchable and spontaneous polarization have strong potential to be utilized in various novel electronic devices. Solid solutions of different perovskite structures induce the coexistence of various phases and enhance the physical functionalities around the phase coexistence region. The construction of phase diagrams is important as they describe the material properties, which are linked to the underpinning physics determining the system. Here we present the phase diagram of (K0.5Na0.5NbO3)–(Ba0.5Sr0.5TiO3) (KNN-BST) system as a function of composition and their associated physical properties. Lead-free (1 − x)KNN–xBST (0 ≤ x ≤ 0.3) solid solution ceramics were synthesized by conventional solid-state reaction technique. The X-ray diffraction and Raman spectroscopic studies indicate composition-dependent structural phase transitions from an orthorhombic phase for x = 0 to orthorhombic + tetragonal dual-phase (for 0.025 ≤ x ≤ 0.15), then a tetragonal + cubic dual-phase (x = 0.2) and finally a cubic single phase for x ≥ 0.25 at room temperature (RT). Among these, the orthorhombic + tetragonal dual-phase system shows an enhanced value of the dielectric constant at room temperature. The phase transition temperatures, orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), decrease with the increase in BST concentrations. The ferroelectric studies show a decrease of both 2Pr and EC values with a rise in BST concentration and x = 0.025 showed a maximum piezoelectric coefficient. [ABSTRACT FROM AUTHOR]

Morphotropic phase boundary (MPB) composition 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 (NBT–6BT) has received industrial acceptance in certain aspects such as ultrasonic cleaners to replace those of lead-based systems. While detailed structure–property analysis on NBT–6BT is mostly confined to room temperature and above, less attention is paid with regard to their structure and property understanding below room temperature. In this work, utilizing the complementarity of Raman spectroscopy, x-ray diffraction, and neutron powder diffraction, we unravel low temperature polar-structural behavior of the MPB composition. While x-ray diffraction shows the persistence of a cubic like global structure in the temperature interval from 300 to 100 K, neutron diffraction reveals a structural crossover from long period modulated to non-modulated P4bm + R3c phase coexistence at ∼150 K. We show that the tendency of growing ferroelectric ordering with reducing temperature is responsible for the structural crossover. Concurrence of weak anomaly in dielectric loss (tan δ) at the same temperature seems to be correlated to the structural crossover. [ABSTRACT FROM AUTHOR]

With increasing industrial acceptance of Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics, there is a need to develop insights into the way different factors influence the microstructural–structural–piezoelectric property correlations. In this work, we have examined the role of structural disorder on the piezoelectric response of the pre-MPB composition x = 0.03 of the well-known solid solution series (1-x)Na0.5Bi0.5TiO3-(x)BaTiO3. Using off-stoichiometry on the A-site as a tuning parameter to vary the structural disorder, which we characterize in terms of the fraction of the "cubiclike phase" or variation in the thermal parameter of the A-site cation, it is shown that the piezo response maximizes for the composition, which retains an optimum degree of disorder after poling. Our study confirms the important role of structural disorder in enhancing piezoelectric response in ferroelectric ceramics. [ABSTRACT FROM AUTHOR]