Growth and electrical performance of Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Fe1/2Nb1/2)O3 single crystals

For the first time, we have grown ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-Pb(Fe_1/2Nb_1/2)O₃ (PMN-PT-PFN) from the melt by the simple slow cooling process. The chemical composition of the single crystals PMN-PT-PFN (0.59/0.31/0.10) is near the morphotropic phase boundary (MPB). X-ray diffraction (XRD) was used to study phase structure of the as-grown crystals, energy dispersive X-ray spectrometer (EDS) and electron probe micro-analyzer (EPMA) were employed to confirm the chemical composition and element distribution of the as-grown crystals, respectively. The ferroelectric, dielectric and piezoelectric properties of the as-grown PMN-PT-PFN (0.59/0.31/0.10) single crystal oriented along the (0 0 1) axis were measured, which showed that the remnant polarization (P_r), coercive electric fields (E_c), the Curie temperature (T_c) and the piezoelectric coefficient (d₃₃) were 50.2 μC/cm², 13.9 kV/cm, 158 °C and about 1800 pC/N, respectively. All the results indicated that the PMN-PT-PFN (0.59/0.31/0.10) single crystals are promising for applying to field of high frequency.     

Electric-field-induced strain and piezoelectric properties of a high Curie temperature Pb(In1/2Nb1/2)O3-PbTiO3 single crystal

The temperature dependence of dielectric and piezoelectric properties, electric-field-induced strains of 0.66 Pb(In_1/2Nb_1/2)O₃-0.34 PbTiO₃ single crystals, which were grown directly from melt by using the modified Bridgman technique with the allomeric Pb(Mg_2/3Nb_1/3)O₃-PbTiO₃ seed crystals, were determined as a function of crystallographic orientation with respect to the prototypic (cubic) axes. Ultrahigh piezoelectric response (d₃₃∼2000 pC/N, k₃₃∼94%) and strain levels up to 0.8%, comparable to rhombohedral (1−x)Pb(Mg_2/3Nb_1/3)O₃-xPbTiO₃ and (1−x)Pb(Zn_2/3Nb_1/3)O₃-xPbTiO₃ single crystals, were observed for the 〈0 0 1〉-oriented crystals. Strain levels up to 0.47% and piezoelectric constant d₃₃∼1600 pC/N could be achieved being related to an electric-field-induced rhombohedral-orthorhombic phase transition for the 〈1 1 0〉-oriented crystals. In addition, high electromechanical coefficients k₃₃ (∼88%) can be achieved even heating to 110 °C. High T_C (∼200 °C), large electromechanical coefficients k₃₃ (∼94%) and low dielectric loss factor (∼1%), along with large strain make the crystals promising candidates for a wide range of electromechanical transducers.     

Triple-like hysteresis loop and microdomain-macrodomain transformation in the relaxor-based 0.76Pb(Mg1/3Nb2/3)O3-0.24PbTiO3 single crystal

Polarization and depolarization behavior of the relaxor-based 0.76Pb(Mg_1/3Nb_2/3)O₃-0.24PbTiO₃ single crystal has been studied between 25 and 200 °C by means of dielectric measurement with or without dc bias, Polarization-Electric field (P-E) hysteresis loop and discharging current measurements. Triple-like P-E loops were obtained in a temperature range between 80 and 90 °C, disclosing the transformation between microdomain state and metastable macrodomain state. For the poled crystals, the microdomain state with dipoles partially oriented was indicated to exist in the similar temperature range and mediate between the lower temperature macrodomain state with dipoles oriented and the higher temperature microdomain state with dipoles in a random system.     

Photoluminescence investigation of rare-earth activated GdCa3(GaO)3(BO3)4 phosphors under UV excitation

A borate compound was adopted as a new host material of Eu³⁺ and Tb³⁺ activators to fabricate efficient luminescence materials. The phosphor compositions, Gd_1−xEu_xCa₃(GaO)₃(BO₃)₄ and Gd_1−xTb_xCa₃(GaO)₃(BO₃)₄, were synthesized by conventional solid-state reactions. The crystalline phases of the resulting powders were identified using an X-ray diffraction system. Their photoluminescence properties were investigated under long-wavelength UV excitation. The Eu³⁺-doped and Tb³⁺-doped GdCa₃(GaO)₃(BO₃)₄ phosphors efficiently emitted red and green light, respectively. The temperature dependency of emission intensity was measured in a range from room temperature to 150 °C. The emission intensities of the red and green phosphors at 150 °C are 87% and 91% of those at room temperature, respectively. In addition, the decay times of both the red and green phosphors are shorter than 3 ms.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Preparation, structure and luminescent properties of a new potassium yttrium borate K3Y3(BO3)4

A new yttrium borate compound K₃Y₃(BO₃)₄ has been obtained in the K₂O-Y₂O₃-B₂O₃ ternary system. Its structure, determined from single crystal X-ray diffraction data, shows that it belongs to space group P2₁/c with unit cell dimensions of a = 10.4667(16) Å, b = 17.361(3) Å, c = 13.781(2) Å and β = 110.548(8)°. The structure consists sheets of [Y₈B₈O₂₄]_∞ linked by out of sheet BO₃ groups and Y ions to form a three-dimensional framework. The luminescent properties of Eu³⁺ and Tb³⁺ doped K₃Y₃(BO₃)₄ materials have also been studied.     

Scintillation and optical properties of Pb-doped YCa4O(BO3)3 crystals

This communication reports optical properties and radiation responses of Pb²⁺ 0.5 and 1.0 mol%-doped YCa₄O(BO₃)₃ (YCOB) single crystals grown by the micro-pulling-down (μ-PD) method for neutron scintillator applications. The crystals had no impurity phases according to the results of X-ray powder diffraction. These Pb²⁺-doped crystals demonstrated blue-light luminescence at 330 nm because of Pb²⁺¹S₀-³P_0,1 transition in the photoluminescence spectra. The main emission decay component was determined to be about 250-260 ns under 260 nm excitation wavelength. When irradiated by a ²⁵²Cf source, the relative light yield of 0.5% Pb²⁺-doped crystal was about 300 ph/n that was determined using the light yield of a reference Li-glass scintillator.     

Thermoluminescence properties of Ce-doped LiSr4(BO3)3 phosphor

Borates LiSr₄(BO₃)₃ were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce³⁺-activated LiSr₄(BO₃)₃ were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce³⁺ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr₄(BO₃)₃:0.01Ce³⁺ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce³⁺.     

Ca4REO(BO3)3 crystals for green and blue microchip laser generation: from crystal growth to laser and nonlinear optical properties

We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca₄REO(BO₃)₃ family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca₄Gd_1−xNd_xO(BO₃)₃) crystals. The process goes from Czochralski boule to 1 × 3 mm² chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca₄Gd_1−xY_xO(BO₃)₃ (Gd_1−xY_xCOB) (x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of ⁴F_3/2 → ⁴I_9/2 Nd³⁺ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO₃) at 930 nm, Nd:YAG (Y₃Al₅O₁₂) at 946 nm, and Nd:ASL (Nd_ySr_1−x La_x−yMg_x Al_12−xO₁₉) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations.     

BaZr(BO3)2: a non-centrosymmetric dolomite-type superstructure

The investigation of the ternary phase diagram for BaOZrO₂B₂O₃ has allowed single crystals to be grown by the flux method with formula BaZr(BO₃)₂. As this composition has been already announced in the literature, but without any structural data, the structure of BaZr(BO₃)₂ has been solved using X-ray data collected on a Kappa CCD diffractometer.This borate crystallizes in the trigonal symmetry with non-centrosymmetric space group R3c (no. 161): a=b=5.167(1) Å and c=33.913(7) Å; Z=6. The structure derived from the dolomite-type with a doubling of the c parameter. Along the c-axis, alternated layers of Ba atoms and Zr atoms are separated by planes of BO₃ groups. BaO₆ and ZrO₆ octahedra so formed are linked by their corners and each Ba(Zr) octahedron is linked to six Zr(Ba) octahedra and to six borate groups. The small deviation from centrosymmetry is attested by considering refinement agreement for the (weak) reflections (h k l) with odd value of l, and positive response of the powder second harmonic generation (SHG) test.A new J.C.P.D.S.-I.C.D.D. card is proposed for this compound.     

Negative thermal expansion in Th2O(PO4)2

High temperature X ray diffraction performed on recently discovered orthorhombic Th₂O(PO₄)₂ shows a continuous linear thermal contraction (−1.6 × 10⁻⁶ °C⁻¹) in 20–600 °C range and a near-zero expansion at higher temperatures resulting from a dual structural deformation involving oxygen oscillations and inter-cations repulsions. Although similar mechanisms were observed in isotypic Zr₂O(PO₄)₂ (+1.5 × 10⁻⁶ °C⁻¹) and U₂O(PO₄)₂ (−1.4 × 10⁻⁶ °C⁻¹), those observed in Th₂O(PO₄)₂ are particularly intense because of the high ionic radius of tetravalent thorium.     

Vacuum ultraviolet excited photoluminescence properties of novel Na3Y9O3(BO3)8:Eu phosphor

The novel vacuum ultraviolet (VUV) excited Na₃Y₉O₃(BO₃)₈:Eu³⁺ red phosphor was synthesized and the photoluminescence (PL) properties were investigated. The phosphor showed strong VUV PL intensity, large quenching concentration (40 mol%) and good chromaticity (0.649, 0.351). The Eu³⁺-O²⁻ charge transition (CT) was observed to be at a higher energy (232 nm, 5.35 eV). The host absorption at 127-166 nm was broad and strong when monitoring the Eu³⁺ emission, which indicated that energy transfer from the host-lattice to the Eu³⁺ ions was efficient in Na₃Y₉O₃(BO₃)₈:Eu³⁺. These excellent VUV PL properties were revealed to be correlated with the unique isolated layer-type structure of Na₃Y₉O₃(BO₃)₈ host. The results showed that the Na₃Y₉O₃(BO₃)₈:Eu³⁺ would be a good candidate for VUV-excited red phosphor.     

Yb-doped NaBi(WO4)2 fibre single crystals grown by the micro-pulling down technique and emission spectroscopic characterization

NaBi_1−xYb_x(WO₄)₂ fibres single crystals were successfully grown by micro-pulling down technology (MPD). The Yb³⁺-doped NaBi(WO₄)₂ fibres single crystals have been pulled using MPD technique with controlled diameter and stationary stable growth conditions corresponding to flat crystallization interface with meniscus length equal to the fibre radii and pulling rate range [6-48 mm h⁻¹]. We have determined the monophased field of NaBi_1−xYb_x(WO₄)₂ for x ≤ 0.3. The lattices parameters decrease as a function of Yb³⁺ substitution in Bi³⁺ sites. The melt behaviour has been study by DTA/TG analysis. We have found that the stoichiometric compounds NaBi(WO₄)₂ melt congruently at 935 °C. The fibre diameters varied from 0.5 to 1 mm depending on the capillary die diameter, pulling rate and the molten zone temperature. Complementary Yb³⁺ spectroscopic characterization in the NaBi(WO₄)₂ lattice has been done by IR emission measurements under laser pumping at room temperature.     

A novel method for preparation of pure Bi2SiO5 crystals

Pure Bi₂SiO₅ crystals were firstly prepared by a novel method of melt-cooling process with Bi₂O₃ and SiO₂ as starting materials. In this study, the preparation and properties of the samples were characterized by thermo gravimetric (TG), differential scanning calorimeter (DSC), field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results showed several endothermic valleys at 579.6 °C, 744.3 °C, 829.3 °C and 879.2 °C during heating process; and a distinct exothermic peak at 805.3 °C during the melt cooling process. XRD and SEM images revealed highly-ordered lamellar pure Bi₂SiO₅ crystals with coarse grains can be achieved by 2 h heating at 805.3 °C.     

Ag-catalyzed synthesis of europium borate Eu(BO2)3 nanowires, growth mechanism and luminescent properties

Eu(BO₂)₃ nanowires with diameters of 10-20 nm were fabricated through direct sintering Eu(NO₃)₃·6H₂O and H₃BO₃ with Ag as catalyst. The result of X-ray diffraction (XRD) indicated that the nanowire was single-crystalline with body-centered monoclinic structure. Based on the fact that Ag nanoparticles attached to the tips and middles of nanowires, a vapor-liquid-solid (VLS) growth mechanism of the Eu(BO₂)₃ nanowires is proposed. Three well-defined stages have been clearly identified during the process: Ag-Eu-B-O cluster process, crystal nucleation, and axial growth. The photoluminescence characteristics under UV excitation were investigated. The dominated Eu³⁺ orange-red emission corresponding to the magnetic dipole transition ⁵D₀ → ⁷F₁ is centered at 591 nm, indicating that Eu³⁺ is located at high symmetry crystal field with inversion center.     

Larger Ba(NO3)2/Sr(NO3)2 crystal growth and solubility determination

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ crystals in aqueous solution from 25 to 65 °C has been determined by both an optical interferometer and a weight technique. A Mach-Zehnder interferometer was used for measuring the concentration distribution of Ba(NO₃)₂ and Sr(NO₃)₂ near the solid/liquid interface during crystal growth and dissolution. A fringe carrier technique was introduced to visualize more clearly the boundary layer and to solve the concentration distribution. Crystals were successfully grown with sizes larger than  mm by a temperature cooling method. The Ba_xSr_1−x(NO₃)₂ crystal was also nucleated and grown. The Raman spectra of Ba_xSr_1−x(NO₃)₂ indicate that the barium ions probably degrade the properties of Sr(NO₃)₂.     

Hydrothermal synthesis and study of an inorganic-organic hybrid vanadate of a nickel(II) coordination complex with pyrazine, Ni3(C4H4N2)3(V8O23)

The three-dimensional hybrid compound Ni₃(C₄H₄N₂)₃(V₈O₂₃) has been synthesized by mild hydrothermal methods under autogenous pressure at 170 °C. The structure of the phase is stable until 380 °C. The removal of the pyrazine molecules from the structure induces its collapse. The IR spectrum shows the vibration modes of the pyrazine molecule and those of the [VO₄]³⁻ groups. A UV-visible spectrum shows the characteristic bands of the Ni(II) d⁸-high-spin cation in a slightly distorted octahedral coordination. Magnetic measurements indicate the existence of antiferromagnetic interactions that can be fitted with a chain model to give g = 2.31, J/k = −5.3, and zJ′/k = −5.5.     

Growth and calorimetric measurements on CsLiB6O10

Single crystals of cesium lithium borate (CLBO) were grown from stoichiometric melt, as well as from B₂O₃ deficient flux. Calorimetric measurements performed on the grown crystals show that the material transforms to glassy phase from the molten phase even at cooling rates as low as 1 °C/min. The transformation to the crystalline phase from the glass phase does not occur during the heating cycle in the DTA experiments. In order to estimate the onset of crystallization temperature of CLBO glass and ensure the appearance of crystallization peak during heating cycle, a new approach (seeded crystallization) was adopted in the DTA experiments. The onset of seeded crystallization temperature shows a strong dependence on the heating and cooling rates. The activation energy of seeded crystallization determined by Kissinger method turns out to be 3.07 eV. The ergodicity making (EM) of the glass transition as seen from the DSC measurement is ∼ 424 °C for a heating rate of 5 °C/min. Microscopic examination suggests that the glass CLBO transforms to crystalline phase via. dendrites.     

Synthesis and microwave dielectric properties of CaO-MgO-SiO2 submicron powders doped with Li2O-Bi2O3 by sol-gel method

Using Ca(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O, Si(OC₂H₅)₄, LiNO₃ and Bi(NO₃)₃·5H₂O as raw materials, CaO-MgO-SiO₂ submicron powders were prepared at low temperature by sol-gel method. The crystallization temperature was decreased enormously by the introduction of Li-Bi liquid phase sintering aids into Ca-Mg-Si sol, and the powders with average particle sizes of 80-100 nm and 200-400 nm were obtained at the calcining temperature of 750 °C and 800 °C, respectively. The sintering characteristic and dielectric properties of powders calcined at 750 °C with different content of powders calcined at 800 °C were studied. When the content of powders calcined at 800 °C was 10 wt%, the dielectric ceramic sintered at 890 °C had compact structure, and possessed excellent microwave dielectric properties: ?_r = 7.16, Q × f = 25630 GHz, τ_f = −69.26 ppm/°C.     

Glass formation tendency in the system SeO2-Ag2O-B2O3

The glass formation regions in the system SeO₂-Ag₂O-B₂O₃ have been determined using the melt quenching method of evacuated silica ampoules. The structural units forming the amorphous network have been established by IR spectroscopy. The presence of SeO₃ (ν = 820 cm⁻¹; 760-750 cm⁻¹), BO₃ (ν = 1340, 1270 cm⁻¹) and BO₄ (ν = 1050 cm⁻¹) units has been confirmed. Crystallization of Ag₂SeO₃ only has been observed in a wide concentrate region near the glass formation boundary. A model explaining the unsatisfactory glass formation ability in the system investigated has been developed. It has been suggested that Ag⁺ ions are predominantly located near the selenite units, which stimulates the formation of isolated SeO₃ groups. The transformation of BO₃ into BO₄ units is hindered by the absence of free Ag⁺ ions near the borate units.