6 MHz BAW resonators fabricated using new piezoelectric crystals PrCa4O(BO3)3 and NdCa4O(BO3)3

Thickness shear mode Bulk Acoustic Wave (BAW) resonators with frequency of 6 MHz, were fabricated using monoclinic piezoelectric crystals PrCa₄O(BO₃)₃ (PrCOB) and NdCa₄O(BO₃)₃ (NdCOB). Zero temperature coefficient of frequency (TCF) characteristics were achieved over the temperature range of –140 °C to 200 °C for (YXt)–1.5° cut PrCOB and (YXt)15° cut NdCOB, with the turnover temperature at 20 °C. The electromechanical coupling factor k₂₆ and the piezoelectric coefficient d₂₆ were determined to be 30.2% and 15.8 pC/N for PrCOB, 29.0% and 15.1 pC/N for NdCOB resonators, respectively. The temperature independent frequency behavior, large coupling factor, high piezoelectric coefficient, together with noticeable mechanical quality factors (Q > 2,500), make PrCOB and NdCOB crystals good candidates for sensing applications with expanded temperature usage range. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Piezoelectric properties of PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics

(1 – x)Pb(Hf_1–yTi_y)O₃–x Pb(Mg_1/3Nb_2/3)O₃ (x = 0.1 ～ 0.25, y = 0.555) ternary piezoelectric ceramics were prepared using the two‐step precursor method. Morphotropic phase boundary (MPB) compositions, located at x = 0.18 ～ 0.22, were confirmed using X‐ray diffraction and by their dielectric, piezoelectric and ferroelectric properties. The optimum dielectric and piezoelectric properties were achieved for the MPB composition 0.8Pb(Hf_0.445Ti_0.555)O₃–0.2Pb(Mg_1/3Nb_2/3)O₃, with dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p and Curie temperature T_C being on the order of 2800, 680 pC/N, 70% and 276 °C, respectively. Of particular significance is that the new ternary ceramics exhibit comparable piezoelectric and electromechanical properties to commercial PZT5H ceramics, but with much improved T_C, showing a potential for applications at elevated temperature. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure,dielectric, and piezoelectric properties of 0.38Bi(Gax Sc1–x )O3–0.62PbTiO3 high temperature piezoelectric ceramics

0.38Bi(Ga_x Sc_1–x )O₃–0.62PbTiO₃ (BGSPTx) ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that BGSPTx has a pure perovskite structure, and the crystal symmetry of BGSPTx changed from rhombohedral to tetragonal with increasing Ga content (x). The Curie temperature (T_C) of BGSPTx ceramics is in the range of 448–467 °C for different x. The ferroelectric phase transition of BGSPTx was found to be of the first order type according to the Curie–Weiss law. For x = 0.125, BGSPTx ceramics show enhanced piezoelectric properties: piezoelectric constant d₃₃ = 420 pC/N and d₃₁ = –142 pC/N, planar and thickness electromechanical coupling factors k_p = 56.27% and k_t = 56.00%, respectively. The high‐T_C of BGSPTx coupled with its excellent piezoelectric properties suggests those future high‐temperature applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of external pressure on Tc of as‐grown and thermally treated superconducting Rbx Fe2–ySe2 single crystals

We report on the effect of external pressure on the superconducting transition temperature (T_c) of as‐grown and thermally treated single crystals of superconducting iron chalcogenide Rb_0.85Fe_1.9Se₂. The superconducting transition temperature of 27.1 K at ambient pressure for the as‐grown sample was found to increase up to 33.2 K for the sample annealed for 3 h at 215 °C in vacuum. An increase of T_c up to 28.2 K was observed for the as‐grown sample at a pressure of 0.83 GPa. For all the studied crystals, annealed in the temperature range between 215 °C and 290 °C, the external pressure seems to decrease the superconducting transition temperature and a negative pressure coefficient of T_c was observed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Piezoelectric and ferroelectric properties of [(K0.4725Na0.4725)Li0.055]NbO3–(Ag0.5Li0.5)TaO3 lead‐free ceramics

New lead‐free piezoelectric (1 – x)[(K_0.4725Na_0.4725)Li_0.055]NbO₃– x (Ag_0.5Li_0.5)TaO₃ [(1 – x)KNNL–x ALT] ceramics were prepared by conventional sintering. Piezoelectric and ferroelectric properties and Curie temperature of the ceramics were studied. The (1 – x)KNNL–x ALT (x = 0.04) ceramics exhibit good properties (d₃₃ ～ 252 pC/N, k_p ～ 41%, T_C ～ 471 °C, T_o–t = 47 °C, P_r = 33.1 μC/cm², E_c = 10.6 kV/cm). These results show that (1 – x)KNNL–x ALT (x = 0.04) ceramic is a promising lead‐free piezoelectric material for high temperature application. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrocaloric effect in antiferroelectric PbZrO3 thin films

Antiferroelectric PbZrO₃ thin films have been deposited on Pt(111)/Ti/SiO₂/Si substrate by polymer modified sol–gel route. Temperature dependent P –E hysteresis loops have been measured at 51 MV/m within a temperature range of 40 °C to 330 °C. The maximum electrocaloric effect ～0.224 × 10^–6 K mV^–1 has been observed near the dielectric phase transition temperature (235 °C) of the thin films. The electrocaloric effect and its strong temperature dependence have been attributed to nearly first‐order phase transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy     

Nitrosation of dialkylhydroxylamines,and computational and NMR investigations of the interconversion of conformational isomers of N‐nitroso‐dimethylhydroxylamine

The effect of acidity upon the rate of nitrosation of N‐benzyl,O‐methylhydroxylamine ( 3 ) in 1:1 (v/v) H₂O/MeOH at 25 °C has been investigated. The pseudo‐first‐order rate constant (k_obs) for loss of HNO₂ as the limiting reagent decreases as [H₃O⁺] increases. This is compatible with two parallel reaction channels (Scheme 2 ). One involves the direct reaction of the free hydroxylamine with HNO₂ (k₁ = 1.4 × 10² dm³ mol^?1 s^?1, 25 °C) and the other involves the reaction of the free hydroxylamine with NO⁺ (k₂ = 5.9 × 10⁹ dm³ mol^?1 s^?1). In contrast, there is only a very slight increase in k_obs with increasing [H₃O⁺] for nitrosation of N,O‐dimethylhydroxylamine ( 4 ) in dilute aqueous solution at 25 °C to give N‐nitroso‐dimethylhydroxylamine, 5 . This also fits a two‐channel mechanism (Scheme 3 ). Again, one involves the nitrosation of the free base by NO⁺ (k₂ = 8 × 10⁹ dm³ mol^?1 s^?1, 25 °C) but the other channel now involves catalysis by chloride (k₃ = 1.3 × 10⁸ dm³ mol^?1 s^?1). Arising from these results, we propose an estimate of pK_a ～ ?5 for protonated nitrous acid, (O = N? OH), which is appreciably different from the literature value of +1.7. The interconversion of cis and trans conformational isomers of 5 has been investigated by temperature‐dependent NMR spectroscopy in CDCl₃, methanol‐d₄, toluene‐d₈ and dimethyl sulfoxide‐d₆. Enthalpies and entropies of reaction and of activation have been determined and compared with computational values obtained at the B3LYP/6‐31G* level of theory. The cis form is slightly more stable at normal temperatures and no solvent effects upon the thermodynamics or kinetics of the conformational equilibrium were predicted computationally or detected experimentally. In addition, key geometric parameters and dipole moments have been calculated for the cis and trans forms, and for the lowest energy transition structure for their interconversion, in the gas phase and in chloroform. These results indicate electronic delocalisation in the ground states of 5 which is lost in the transition structure for their interconversion. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure and piezoelectric properties of BiFeO3 and Bi0.92Dy0.08FeO3 multiferroics at high temperature

Multiferroic BiFeO₃ and Bi_0.92Dy_0.08FeO₃ ceramics were prepared to study their crystal structures and piezoelectric properties. BiFeO₃ exhibits rhombohedral phase below 810 °C. Although Bi_0.92Dy_0.08FeO₃ ceramic also shows rhombohedral phase at room temperature, it allows the coexistence of rhombohedral phase and orthorhombic phase at 460–650 °C. Both samples have maximum polarizations of >21 μC/cm² and piezoelectric d₃₃ values of ～37 pC/N at room temperature. Their polarized slices show the dielectric anomalies and impedance anomalies because of vibrating resonances below 500 °C, and the thickness vibration electromechanical coupling factor is ～0.6 and ～0.4 for BiFeO₃ and Bi_0.92Dy_0.08FeO₃, respectively. The vibrating resonances confirm piezoelectric responses. Furthermore, samples' impedance and resistance decrease fast with temperature increasing, which screens piezoelectric response above 550 °C.     

Effects of Li Substitution and Sintering Temperature on Properties of Bi0.5（Na,K）0.5TiO3 Lead-Free Piezoelectric Ceramics

Bi0.5 （Na0.72K0.28- x Lix ）0.5 TiO3 （BNKLT- 100x） lead-free piezoelectric ceramics are synthesized by conventional solid state sintering techniques. The dielectric and piezoelectric properties of the BNKLT-100x ceramics as a function of Li content are systematically investigated. It is found that not only Li content but also the sintering temperature has a strong effect on the piezoelectric properties of BNKLT. The piezoelectric constant d33 Of BNKLT varies from 120 to 252pC/N in the Li content range from 0.03 to 0.16. In the sintering temperature range from 1080 to 1130℃, the d33 value of BNKLT-6 changes from 200pC/N to 252pC/N. The BNKLT-6 sample sintered at 1100℃ has the highest piezoelectric constant d33 of 252pC/N, with the electromechanical coupling factors kp of 0.32 and kt of 0.44.     

Dielectric,ferroelectric and piezoelectric properties of (1−x)[K0.5Na0.5NbO3]−x[LiSbO3] ceramics

Lead-free (1?x)[K_0.5Na_0.5NbO₃]?x[LiSbO₃] (x=0, 0.04, 0.05 and 0.06)/(KNN-LS) ceramics were prepared by conventional solid-state reaction route (CSSR). For dense morphology pure KNN ceramic was sintered at 1120 °C and LS modified KNN ceramics were sintered at 1080 °C for 4 h, respectively. The structural study at room temperature (RT) revealed the transformation of pure orthorhombic to tetragonal structure with the increase in LS content in KNN-LS ceramics. Temperature dependent dielectric study confirmed the increase of diffuse phase transition nature with the increase in LS content in KNN-LS ceramics. The presence of orthorhombic to tetragonal (T_O?T) polymorphic phase transition temperature (PPT) ～43 °C confirmed the presence of two ferroelectric (orthorhombic and tetragonal) phases in 0.95KNN-0.05LS ceramics at RT. 0.95KNN-0.05LS ceramics showed better ferroelectric and piezoelectric properties i.e., remnant polarization (P_r)～18.7 μC/cm², coercive field (E_c)～11.8 kV/cm, piezoelectric coefficient (d₃₃)～215 pC/N, coupling coefficient (k_p)～0.415 and remnant strain ～0.07% were obtained.     

Effect of temperature–bias annealing on the hysteresis and subthreshold behavior of multilayer MoS2 transistors

The transfer characteristics (I_D–V_G) of multilayers MoS₂ transistors with a SiO₂/Si backgate and Ni source/drain contacts have been measured on as‐prepared devices and after annealing at different temperatures (T_ann from 150 °C to 200 °C) under a positive bias ramp (V_G from 0 V to +20 V). Larger T_ann resulted in a reduced hysteresis of the I_D–V_G curves (from ～11 V in the as‐prepared sample to ～2.5 V after T_ann at 200 °C). The field effect mobility (～30 cm² V^–1 s^–1) remained almost unchanged after the annealing. On the contrary, the subthreshold characteristics changed from the common n‐type behaviour in the as‐prepared device to the appearance of a low current hole inversion branch after annealing. This latter effect indicates a modification of the Ni/MoS₂ contact that can be explained by the formation of a low density of regions with reduced Schottky barrier height (SBH) for holes embedded in a background with low SBH for electrons. Furthermore, a temperature dependent analysis of the subthreshold characteristics revealed a reduction of the interface traps density from ～9 × 10¹¹ eV^–1cm^–2in the as‐prepared device to ～2 × 10¹¹ eV^–1cm^–2after the 200 °C temperature–bias annealing, which is consistent with the observed hysteresis reduction.

Schematic representation of a back‐gated multilayer MoS₂ field effect transistor (left) and transfer characteristics (right) measured at 25 °C on an as‐prepared device and after the temperature–bias annealing at 200 °C under a positive gate bias ramp from 0 V to +20 V.     

Elastic,piezoelectric and dielectric properties of ZnO and CdS single crystals in a wide range of temperatures

A complete set of elastic, piezoelectric and dielectric constants of ZnO and CdS at room temperature was determined by the method of resonance-antiresonance. Elastic constants s^E₁₁, s^E₁₂, s^E₅₅, c^D₃₃, c^D₅₅, coefficients of electromechanical couplingk₃₁, k₁₅, k_t and dielectric constants ε^T₁₁, ε^T₃₃ of ZnO single crystals were determined in the temperature range 4.2–800 K. Elastic constants s^E₁₁, s^E₁₂, s^D₃₃, s^E₅₅, s^D₃₃, s^D₅₅, coefficients of electromechanical coupling k₃₁, k₃₃, k₁₅, k_t and dielectric constants ε^T₁₁, ε^T₃₃ of CdS single crystals were determined in the temperature range 4.2–300 K.     

Piezoelectric activity and phase transitions in (PMN)0.69(PT)0.31 single crystal

Piezoelectric and dielectric investigations have been performed on a (PMN)_0.69(PT)_0.31 single crystal. Low frequency (100?Hz) dielectric permittivity measurements revealed distinct anomaly at 129°C (T _εmax) corresponding to the structural transformation from the tetragonal to cubic phase. Two other anomalies have been detected at 90 and 96°C. After preliminary polarization in the d.c. electric field, switched on above T _εmax and switched off inside the tetragonal phase, the piezoelectric activity has been observed in function of temperature. Values of the piezoelectric resonance frequencies changed markedly at 96°C (on cooling) and 124°C (on heating) showing clear softening of the elastic properties near these temperatures. Values of the piezoelectric and electromechanical coupling coefficients obtained were respectively of the order of 800?pCN^?1 (d ₃₁) and 0.35?(k ₃₁). Piezoelectric activity was detected tens of degrees above the temperature T _εmax and disappeared at temperature at which the dispersion of the dielectric permittivity due to the presence of polar nanoregions is negligible. It was found that strong softening of the elastic properties accompanies phase transitions to the tetragonal and monoclinic phase.     

Electrical properties of high Curie temperature (1−x)Pb(In1/2Nb1/2)O3-xPbTiO3 single crystals grown by the solution Bridgman technique

0.65Pb(In_1/2Nb_1/2)O₃-0.35PbTiO₃ (PINT65/35) (starting composition) single crystals were grown successfully through the solution Bridgman technique using PbO flux and PMNT67/33 seed crystals. Because of the composition variation, the final composition of achievable crystals is in a range of 0.32-0.34 with the corresponding T_c range of 265-269 °C. The (001) plates of as-grown PINT66/34 single crystals show high Curie temperature (T_c=269 °C) and rhombohedral-tetragonal phase transition temperature (T_rt=134 °C). Besides, good electrical properties with high dielectric constant (ε>3000), low dielectric loss (tan δ∼1.2%), high piezoelectric constant (d₃₃∼2000 pC/N) and large electromechanical coupling factor (k_t≈59%) at room temperature have been obtained on the (001) plates. The sound velocity, acoustic impedance and other piezoelectric parameters were also measured on the (001) plates in this study, which provide us more detailed information about PINT66/34 single crystals.     

High‐performance In–Zn–O thin‐film transistors with a soluble processed ZrO2 gate insulator

Spin‐coated zirconium oxide films were used as a gate dielectric for low‐voltage, high performance indium zinc oxide (IZO) thin‐film transistors (TFTs). The ZrO₂ films annealed at 400 °C showed a low gate leakage current density of 2 × 10^–8 A/cm² at an electric field of 2 MV/cm. This was attributed to the low impurity content and high crystalline quality. Therefore, the IZO TFTs with a soluble ZrO₂ gate insulator exhibited a high field effect mobility of 23.4 cm²/V s, excellent subthreshold gate swing of 70 mV/decade and a reasonable I_on/off ratio of ～10⁶. These TFTs operated at low voltages (～3.0 V) and showed high drain current drive capability, enabling oxide TFTs with a soluble processed high‐k dielectric for use in backplane electronics for low‐power mobile display applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric and piezoelectric properties of manganese‐modified PbHfO3–PbTiO3–Pb(Mg1/3Nb2/3)O3 ternary ceramics with morphotropic phase boundary compositions

High piezoelectric and electromechanical properties were reported in the PbHfO₃–PbTiO₃–Pb(Mg_1/3Nb_2/3)O₃ ternary system with morphotropic phase boundary (MPB) compositions. This work focuses on the effect of MnO₂ addition on 0.8Pb(Hf_0.443Ti_0.557)O₃–0.2PMN (0.8PHT–0.2PMN) ceramics. It was observed that the Mn acceptor modification induced a “hardening” effect in 0.8PHT–0.2PMN, with decreased piezoelectric coefficients d₃₃ and dielectric loss tan δ and a significantly increased mechanical quality factor Q_m. Moreover, the 0.2 wt% MnO₂‐doped 0.8PHT–0.2PMN ceramics exhibited good piezoelectric and electromechanical properties with d₃₃, planar electromechanical coupling k_p and Q_m being on the order of 360 pC/N, 61% and 700, respectively, showing advantages compared to those of commercial hard PZT4 ceramics, which is attractive for high power applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Li‐, Sb‐ and Ta‐modified (K,Na)NbO3 nanopowder prepared via a water‐based sol–gel method

Stable Li‐, Sb‐ and Ta‐modified (K, Na)NbO₃ (LTS‐KNN) sol and gel were successfully prepared via an economical water‐based sol–gel method. Simultaneous thermogravimetry and differential scanning calorimetry (TG‐DSC) and X‐ray diffraction showed that organic compounds were eliminated and a pure perovskite phase formed around 600 °C. Transmission electron microscopy showed that the LTS‐KNN particle size was in the range of 11–34 nm after decomposition at 600 °C. Moreover, high performance LTS‐KNN ceramic was successfully prepared at a low sintering temperature of 1000 °C by use of the nanopowder, and its room‐temperature d₃₃, K_p, K and loss are 311 pC/N, 46.8%, 1545 and 0.024, respectively. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observation of insulating–insulating monoclinic structural transition in macro‐sized VO2 single crystals

VO₂ single crystals with unprecedented quality, exhibiting a first‐order metal–insulator transition (MIT) at 67.8 °C and an insulator –insulator transition (IIT) at ～49 °C, are grown using a self‐flux evaporation method. Using synchrotron‐based X‐ray microdiffraction analysis, it is shown that the IIT is related to a structural phase transition (SPT) from the monoclinic M2 phase to the M1 phase upon heating while the MIT occurs together with a SPT of M1 to the rutile R phase. All previous reports have shown that VO₂ exists in the M1 phase at room temperature in contrast to the M2 phase observed in this work. We suggest that internal strain inside single crystal VO₂ may generate the previously unobserved IIT and the unusual room temperature structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spin‐dependent‐magnetoresistance control by regulation of heat treatment temperature for magnetite nano‐particle sinter

The control of spin‐dependent‐magnetoresistance by regulation of the heat treatment (HT) temperature for magnetite (Fe₃O₃) nano‐particle sinter (MNPS) has been studied. The average nano‐particle size in the MNPS is 30nm and the HT was carried out from 400°C to 800°C. The HT of the MNPS varies the coupling form between adjacent magnetite nano‐particles and the crystallinity of that. The measurements on electrical resistance (ER), magnetoresistance (MR) and magnetization were performed between 4K and 300K. The behavior of the ER and MR considerably changes at the HT temperature of ～600°C. Below ～600°C the ER indicates the variable‐range‐hopping conduction behavior and the MR shows the large intensity in a wide temperature region. Above ～600°C the ER shows the indication of the Verwey transition near 110K like a bulk single crystal and the MR designates the smaller intensity. We consider that below ～600°C the ER and MR are dominated by the grain‐boundary conduction and above ～600°C those are determined by the inter‐grain conduction. The magnetic field application to the grain‐boundary region is inferred to cause the large enhancement of the MR.