Structural,ferroelectric, optical properties of A-site-modified Bi0.5(Na0.78K0.22)0.5Ti0.97Zr0.03O3 lead-free piezoceramics

We reported the role of A-site modification on the structural, ferroelectric, optical and electrical field-induced strain properties of Bi_0.5(Na_0.78K_0.22)_0.5Ti_0.97Zr_0.03O₃ lead-free piezoceramics. The Li⁺ ions with concentration from 0 to 5 mol% were used to substitute at A-site. There was no phase transition when Li⁺ ions was added up to 5 mol%. The electric field-induced strain (S_max/E_max) values increased from 600 to 643 pm/V for 2 mol% Li⁺-added which results from distortion both rhombohedral and tetragonal phase structures. The band gap reduced from 2.88 to 2.68 eV and the saturation polarization decreased from 46.2 to 26.1 μC/cm² when Li⁺ ions concentration increased from 0 to 5 mol% respectively. We expect that this work could be helpful for further understanding the role of A-site dopants in comparison with B-site modification in lead-free Bi_0.5(Na,K)_0.5TiO₃-based ceramics.     

Effect of Li2CO3 addition on the structural,optical, ferroelectric,and electric-field-induced strain of lead-free BNKT-based ceramics

In this work, we reported the effect of Li₂CO₃ addition on the structural, optical, ferroelectric properties and electric-field-induced strain of Bi_0.5(Na,K)_0.5TiO₃ (BNKT) solid solution with CaZrO₃ ceramics. Both rhombohedral and tetragonal structures were distorted after adding Lithium (Li). The band gap values decreased from 2.91 to 2.69 eV for 5 mol% Li-addition. The maximum polarization and remanent polarization decreased from 49.66 μC/cm² to 27.11 μC/cm² and from 22.93 μC/cm² to 5.35 μC/cm² for un-doped and 5 mol% Li- addition BNKT ceramics, respectively. The maximum S_max/E_max value was 567 pm/V at 2 mol% Li₂CO₃ access. We expected this work will help to understand the role of A-site dopant in lead-free ferroelectric BNKT materials.     

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na⁺–Li⁺ ion exchange, electrical conductivity, and mechanical relaxation have been studied below T_g on glasses of the system ZrF₄–BaF₂–LaF₃–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na⁺–Li⁺ ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F⁻ and Li⁺ ions to the transport. Moreover, the presence of the three partially interacting mobile species F⁻, Na⁺, Li⁺ obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li⁺ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li⁺ movement via energetically suitable sites near F⁻ ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.     

Structural,XPS and impedance analysis of LixCoVO4 (x = 0.8, 1.0, 1.2)

Lithium cobalt vanadate Li_xCoVO₄ (x = 0.8; 1.0; 1.2) has been prepared by a solid state reaction method. The XRD analysis confirms the formation of the sample. A new peak has been observed for Li_1.0CoVO₄ and for Li_1.2CoVO₄ indicating the formation of a new phase. The XPS analysis indicates the reduction in the oxidation of vanadium and oxygen with the addition of Li in Li_xCoVO₄ (x = 0.8, 1.0, 1.2). The impedance analysis gives the conductivity value as 2.46 × 10^− 5, 6.16 × 10^− 5, 9 × 10^− 5 Ω^− 1 cm^− 1 for Li_xCoVO₄ (x = 0.8; 1.0; 1.2), all at 623 K. The similarity in the bulk activation energy (E_a) and the activation enthalpy for migration of ions (E_ω) indicate that the conduction in Li_1.2CoVO₄ has been due to hopping mechanism.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.     

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li6CaLa2Ta2O12 and Li6BaLa2Ta2O12

High-purity specimens of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li₆CaLa₂Ta₂O₁₂ and a = 13.001(4) Å for Li₆BaLa₂Ta₂O₁₂. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li⁺ ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ samples exhibit the conductivity σ = 2.2 × 10^? 6 S cm^? 1 at 27 °C (E_a = 0.50 eV) and σ = 1.3 × 10^? 5 S cm^? 1 at 25 °C (E_a = 0.44 eV), respectively.     

Effect of Li2O on the structure,electrical and dielectric properties of xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 glasses

Glasses of the general formula xLi₂O·(20?x)CaO·30P₂O₅·30V₂O₅·20Fe₂O₃ with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P₂O₇)^4?, FeO₆, V–O^? and PO^? groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li₂O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V⁴⁺ to V⁵⁺. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li₂O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li₂O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively.     

Mechanoluminescence characterisation of γ-irradiated (KNa)Br:Ce3+ phosphor

The mechanoluminescence (ML) of γ-irradiated coloured powder of (KNa)Br:Ce(0.1–10 mol%) phosphor is reported in this paper. The samples are prepared by wet chemical method. The ML intensities are found to be dependent on concentrations of Ce³⁺ ion and γ-rays radiation dose. The variation of peak ML intensity of (KNa)Br:Ce(0.5 mol%) with different γ-rays dose is found as linear up to 2.5 kGy high dose from 0.08 kGy, whereas for the KBr:Ce(0.5 mol%) and NaBr:Ce(0.5 mol%) samples the ML intensities increases sublinearly. The prepared sample shows minimum fading in ML intensity. The ML characterisation shows the good linearity, less fading and simple ML glow curve structure, thus the prepared material may be useful for radiation dosimetry.     

Ag8SnSe6 argyrodite synthesis and optical properties

The Ag₈SnSe₆ argyrodite compound was synthesized by the direct melting of the elementary Ag, Sn and Se high purity grade stoichiometric mixture in a sealed silica ampoule. The prepared polycrystalline material was characterized by the X-ray diffraction (XRD), visible (VIS) and near-infrared (NIR) reflection and photoluminescence (PL) spectroscopy. XRD showed that the Ag₈SnSe₆ crystallizes in orthorhombic structure, Pmn2₁ space group with lattice parameters: а = 7.89052(6) Å, b = 7.78976(6) Å, c = 11.02717(8) Å. Photoluminescence spectra of the Ag₈SnSe₆ polycrystalline wafer show two bands at 1675 nm and 1460 nm. Absorption edge position estimated from optical reflectance spectra is located in the 1413–1540 nm wavelength range.     

A single-crystal study of the electrochemically Li-ion intercalated spinel-type Li4Ti5O12

Single crystals of Li_4 + xTi₅O₁₂ were prepared by means of electrochemical Li-ion intercalation technique using parent Li₄Ti₅O₁₂ single crystals. The obtained Li_4 + xTi₅O₁₂ (x = 1.35) crystallizes in the cubic spinel-related type structure, space group Fd3?m, and lattice parameters of a = 8.346(2) Å and V = 581.3(5) Å³ and Z = 8. The Li-ion intercalated sites were successfully determined to be both the 8a and 16c sites by using the difference Fourier synthesis map. The structure was determined by single-crystal X-ray structure analysis and refined to the conventional value of R = 3.7% for 132 independent observed reflections. The chemical composition has been determined to be Li_5.35Ti₅O₁₂ from the result of site-population refinements. In addition, theoretical electron density distributions and total energy were calculated for three postulated compounds of “Li_4.5Ti_4.5O₁₂” and “Li_4.5 + xTi_4.5O₁₂” with x = 1.5 and 3.0.     

Mixed ion-polaron transport in lithium vanadium–molybdenum tellurite glasses

The electrical properties of mixed ion-polaron conducting vanadium tellurite glasses of the form XLi₂O·(1 − X)[0.5V₂O₅·0.5MoO₃]2TeO₂ have been studied by using the impedance spectroscopy in a wide range of temperature and composition. The obtained results confirm the existence of a transition from a typically electronic (polaronic) conductive regime when the molar fraction (X) of Li₂O is equal to 0, to an ionic conductive regime when X tends to 1. This transition is characterised by a deep minimum in the electrical conductivity of about 3 orders of magnitude. The correlated behaviour between conductivity and the mean distance between lithium ions and between vanadium ions reinforces the key idea of two independent migrating paths for both electrons and ions, respectively.     

High peak power 16 μm InP-related quantum cascade laser

In this paper ～16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ～ 15.6 μm (641 cm^?1) and at λ ～ 16.6 μm (602 cm^?1) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ～15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.     

High lithium ion conducting glass-ceramics in the system Li2S–P2S5

Highly ion-conductive Li₂S–P₂S₅ glass-ceramic electrolytes were prepared by controlling the compositions and heat treatment temperatures of the glasses. The 70Li₂S·30P₂S₅ (mol%) glass-ceramic heated at 360 °C showed the highest conductivity of 3.2 × 10^− 3 S cm^− 1 at room temperature and the lowest activation energy of 12 kJ mol^− 1 for conduction in the binary system Li₂S–P₂S₅. The outstanding property was attributed to both the precipitation of the new crystal as a metastable phase and the increase in crystallinity of the phase. With increasing heat treatment temperatures, the metastable phase changed into thermodynamically stable phases such as the Li₄P₂S₆ crystal by heat treatment up to 550 °C, resulting in low conductivities of the glass-ceramics. It was, thus, found that the formation of superionic metastable phases by heating the Li₂S–P₂S₅ glasses is responsible for the marked enhancement on the conducting properties of the glass-ceramics.     

Preparation of phase pure and well-crystallized Li4Ti5O12 nanoparticles by precision control of starting mixture and calcining at lowest possible temperatures

In an attempt to obtain spinel Li₄Ti₅O₁₂ with smallest possible grain size and highest possible phase purity via a solid state route, we tried to elevate reactivity of the reactant mixture by mechanical activation and appropriate choice of the starting materials. From the stoichiometric mixture comprising Li₂CO₃ and 150 nm anatase, we needed to heat at 950 °C for 1 h to obtain 81–88% phase purity (PhP) of Li₄Ti₅O₁₂ with its average grain size ca 600 nm. After mechanical activation with a multi-ring mill for 30 min, 850 °C was enough to obtain 85–87% pure 500 nm spinel. From a combination of LiNO₃ and 50 nm anatase, 90–91% phase pure product with its grain size 240 nm was obtained at 750 °C due to fusion of the nitrate and shorter diffusion path. By using CH₃COOLi.2H₂O and 50 nm anatase we obtained 130 nm Li₄Ti₅O₁₂ with its PhP ca 90% by milling the mixture preliminarily calcined at 500 °C for 1 h and heating subsequently at 700 for 1 h.     

Modelling the directional and energy dependence of 5–10 keV Ar+ ion-induced secondary electron yields from Cu crystals

The primary ion directional effects observed in secondary electron yields induced by ion bombardment [5 keV Ar⁺ → Cu(100)] are simulated using a semi-empirical molecular dynamics model. The directional effects are presumed to arise from inelastic energy transfers that take place in close binary atomic encounters. The latter are estimated using the Oen-Robinson model, in combination with a critical apsidal distance (R_c). The connection between the measured kinetic electron emission (KEE) yields (γ_KEE) and the predicted inelastic energy loss in a binary atomic collision (ΔE_i) is established through a semi-empirical fitting procedure involving R_c and other parameters in the following model: γ_e = γ₀ + γ_KEE = γ₀ + 〈ΔE_i(z)exp(? z/λ)〉, where z is the collision depth. The directional effects are best reproduced by fitting the model to Ar–Cu inelastic collisions for two azimuthal incident directions: R_c is estimated to be 0.47 ± 0.03 Å; the parameter, λ (an effective electron attenuation length), is estimated to be 18 ± 2 Å. The same model also describes the γ_KEE energy dependence for 5–10 keV Ar⁺ normally incident on low-index Cu crystal targets [Phys. Rev. 129 (1963) 2409]. The spatial and temporal distributions of the hard collisions that initiate KEE are discussed on the basis of the model.     

Improvement of stability and pulse energy in a diode-pumped dual-loss-modulated QML Nd:Lu0.2Y0.8VO4 laser with EO modulator and GaAs

The Q-switched and mode-locked (QML) performance in a diode-pumped Nd:Lu_0.2Y_0.8VO₄ laser with electro-optic (EO) modulator and GaAs saturaber absorber is investigated. In comparison with the solely passively QML laser with GaAs, the dual-loss-modulated QML laser with EO and GaAs can generate pulses with higher stability and shorter pulse width of Q-switched envelope, as well as higher pulse energy. At the repetition rate 1 kHz of EO, the pulse width of Q-switched pulse envelope has a compression of 89% and the pulse energy has an improvement of 24 times. The QML laser characteristics such as the pulse width, pulse peak power etc. have been measured for different small-signal transmittance (T₀) of GaAs, different reflectivity (R) of output coupler and modulation frequencies of the EO modulator (f_e). The highest peak power and the shortest pulse width of mode-locked pulses are obtained at f_e = 1 kHz, R = 90% and T₀ = 92.6%. By considering the influences of EO modulator, a developed rate equation model for the dual-loss-modulated QML laser with EO modulator and GaAs is proposed. The numerical solutions of the equations are in good agreement with the experimental results.     

Submillimeter-wave measurements of N2 and O2 pressure broadening for HO2 radical generated by Hg-photosensitized reaction

The N₂ and O₂ pressure broadening coefficients of the pure rotational transitions at 625.66 GHz (N_KaKc=10_1?9–10_0?10, J=10.5–10.5) and 649.70 GHz (N_KaKc=10_2?9–9_2?8, J=9.5–8.5) in the vibronic ground state X²A′ of the perhydroxyl (HO₂) radical have been determined by precise laboratory measurements. For the production of HO₂, the mercury-photosensitized reaction of the H₂ and O₂ precursors was used to provide an optimum condition for measurement of the pressure broadening coefficient. The Superconducting Submillimeter-wave Limb Emission Sounder (SMILES) was designed to monitor the volume mixing ratio of trace gases including HO₂ in the Earth's upper atmosphere using these transitions. The precise measurement of pressure broadening coefficient γ in terms of the half width at half maximum is required in order to retrieve the atmospheric volume mixing ratio. In this work, γ coefficients of the 625.66 GHz transition were determined for N₂ and O₂ at room temperature as γ(N₂)=4.085±0.049 MHz/Torr and γ(O₂)=2.578±0.047 MHz/Torr with 3σ uncertainty. Similarly, the coefficients of the 649.70 GHz transition were determined as γ(N₂)=3.489±0.094 MHz/Torr and γ(O₂)=2.615±0.099 MHz/Torr. The air broadening coefficients for the 625.66 GHz and 649.70 GHz lines were estimated at γ(air)=3.769±0.067 MHz and 3.298±0.099 MHz respectively, where the uncertainty includes possible systematic errors. The newly determined coefficients are compared with previous results and we discuss the advantage of the mercury-photosensitized reaction for HO₂ generation. In comparison with those of other singlet molecules, the pressure broadening coefficients of the HO₂ radical are not much affected by the existence of an unpaired electron.     

The effect of dispersed SrTiO3 particles on the ionic conduction of (La,Li)Ti2O6

Ionic conductivity of La_4/3 ? y Li_3yTi₂O₆ (LLTO), where y value is 0.21, dispersed by various amount of strontium titanate (SrTiO₃) was measured by complex impedance method, and powder X-ray diffraction (XRD) measurements and scanning electron microscope (SEM) observations were carried out. With increasing SrTiO₃ concentration, the conductivity decreased. At 34 mol%, the Bragg peaks at 11, 26 and 35° in LLTO disappeared in XRD patterns and small non-angulated crystals were shown in SEM. The behavior of ionic conductivity was discussed by using the effective medium approximation (EMA) theory.     

Effect of Li-substitution on piezoelectric and ferroelectric properties of (Bi0.92Na0.92−xLix)0.5Ba0.06Sr0.02TiO3 lead-free ceramics

New lead-free ceramics (Bi_0.92Na_0.92−xLi_x)_0.5Ba_0.06Sr_0.02TiO₃ have been fabricated by a conventional ceramic technique and their electrical properties have been studied. X-ray diffraction studies reveal that Li⁺, Ba²⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure. The partial substitution of Li⁺ for Na⁺ increases the remanent polarization P_r of the ceramics. Because of the large P_r and low coercive field E_c, the ceramics with x = 0.075–0.125 exhibit excellent piezoelectric properties: d₃₃ = 189–235 pC/N, k_p = 33.6–36.3% and k_t = 51.6–54.3%. The ceramics exhibit relaxor behaviors after the substitution of Li⁺ for Na⁺. Our results also suggest that polar and non-polar phases may coexist in the ceramics at temperatures above the depolarization temperature T_d.     

TL and OSL studies on lithium borate single crystals doped with Cu and Ag

Lithium borate (LBO) single crystals doped with Cu and Ag (0.25 mol% each) (Li₂B₄O₇:Cu,Ag) are grown by the Czochralski method. The thermoluminescence readout on Li₂B₄O₇:Cu,Ag crystals showed three glow peaks at～375, 441 and 516 K for the heating rate of 1  K/s. The thermoluminescence sensitivity of the grown Li₂B₄O₇:Cu,Ag single crystals is found to be 5 times TLD-100 and a linear dose response in the range 1 mGy to 1 kGy. The glow curve deconvolution reveals nearly first order kinetics for all the three peaks with trap depths 0.77, 1.25 and 1.34 eV respectively and corresponding frequency factors 1.6×10⁹, 1.3×10¹³ and 6.8×10¹¹ s^?1. The continuous wave optically stimulated luminescence (CW-OSL) measurements were performed on the LBO:Cu,Ag single crystals using blue light stimulation. The traps responsible for the three thermoluminescence peaks in Li₂B₄O₇:Cu,Ag are found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response is established. The photoluminescence studies show that in case of co-doping of Ag in LBO:Cu the emission at 370 nm in Cu states dominates over the transitions in Ag states implying doping of Ag plays a role as sensitizer when co-doped with Cu and increases overall emission.