Crystal growth and electric‐property change by rubidium or cesium doping on potassium‐sodium‐niobate

Alkali metals (Na, Rb or Cs) co‐doped with fiber‐ and bulk‐shaped KNbO₃ single crystals were grown using two original methods by means of doping together of small ionic Na and large ionic Rb or Cs into KNbO₃. Single‐phase crystals could be grown with an orthorhombic system at room temperature as well as pure KNbO₃. Piezoelectric and ferroelectric property changes by the co‐doping of Rb or Cs with Na were estimated using d₃₃ values and a polarization‐electric field hysteresis curve in fiber‐ and bulk‐shaped crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and phase transitions of oxide-ion conducting compound La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> doped with alkaline metals

The specific features of synthesis, polymorthism, and electric conductivity of oxide-ion conducting compounds La_{2 − x} Me _x Mo₂O_{9 − y} , where Me = Na, K, Rb, or Cs, have been studied. Ceramic samples were obtained by solid-state synthesis in the temperature range of 960–1100°C. The regions where solid solutions exist have been found to depend on the temperature of the sample firing. According to the calorimetric and electrophysical data, the phase transition from the monoclinic phase (α) to the cubic phase (β) in samples doped with potassium and rubidium disappears at x = 0.02 and 0.04, respectively. In these cases the only transition from the cubic β _ms phase to the high-temperature cubic β phase is observed near 450°C. Doping with sodium and cesium does not suppress the α → β phase transition.     

Structure and morphological stability of (Lu1–xEux)2O3 thin films

(Lu_1–xEu_x)₂O₃ smooth, crack‐free, transparent films were prepared by the Pechini sol–gel method and a spin‐coating technique. Thermogravimetric analysis, differential thermal analysis and FITR spectroscopy were used to study the chemical processes during annealing of the films. Film structure, morphology and optical properties were investigated. X‐ray diffraction (XRD) analysis reveals the cubic phase of (Lu_1–xEu_x)₂O₃ films annealed in the 600–1000 °C temperature range. Smooth and crack‐free films with thicknesses of 250–1000 nm were obtained in the 600–800 °C temperature range. The thickness upper limit (1000 nm) of morphological stability of films (Lu_1–xEu_x)₂O₃ on sapphire substrates has been studied.     

XRD,IR, and Raman investigations of structural properties of Dy2‐xHox O3 prepared by sol gel procedure

The Rare earth mixed oxides Dy_2‐xHo_x O₃ (0.0 ≤ x ≤ 2.0) solid solution was synthesized by a sol–gel process. X‐ray diffraction (XRD) data were collected and crystal structure and microstructure analyses were performed applying Rietveld refinement method. Infrared and Raman spectroscopy were used to define the microstructure and to locally probe the structure of the samples. The cationic distribution over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be randomly. The crystallite size and microstrain as well as Raman modes positions are influenced by Ho³⁺ concentration. The apparent size is isotropic but significant anisotropy is found for the microstrain with its largest value along the crystallographic direction [h00]. Inspite the single phase solid solution confirmed by Rietveld analysis for all samples, Raman spectra detected the coexistence of two phases; cubic and distorted monoclinic of too small amount or highly disordered, i.e. amorphous like, to be detected by XRD. The result indicates the ability of Raman spectroscopy to detect minor phases in solid solutions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the temperature and the oxygen partial pressure on the phase formation in the system Cu – Fe – O

Copper iron oxides, Cu_1‐xFe_2+xO₄ (0 ≤ x ≤ 0.5), have been synthesized by thermal oxidation of copper ‐ iron mixtures. In this process, the phase formation and the phase stability were investigated as function of the temperature (800°C – 1200°C) and the oxygen partial pressure (1.013 x 10¹ – 1.013 x 10⁵ Pa). The phase formation starts with the reaction of the metallic components to simple oxides (Fe₃O₄, Fe₂O₃, CuO). From these simple oxides, the formation of complex oxides requires a minimum temperature of 800°C. The synthesis of single phase spinel compounds Cu²⁺_1‐2x Cu¹⁺_xFe_2+xO_4±δ is realized for 0.1 ≤ x ≤ 0.5, using specific temperature – p(O₂) – conditions for a given value of x. Remarkably, to achieve our goal, we found that the increase of x implies that of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. Besides, a single phase spinel CuFe₂O₄ does not exist in the temperature / p(O₂)‐field investigated. Using the results of XRD ‐ phase analysis, T ‐ p(O₂) – x – diagrams were constructed. These diagrams allow the prediction of phase compositions expected for different synthesis conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of rapid thermal annealing on Zn1‐xCdxO layers grown by radio‐frequency magnetron co‐sputtering

Zn_1‐xCd_xO layers were deposited on the sapphire substrate using the radio‐frequency magnetron co‐sputtering system. The grown Zn_1‐xCd_xO layers were carried out in the post‐annealing treatment for 1 min at the 800 °C oxygen‐ambient by the rapid thermal annealing (RTA) method. X‐ray diffraction (XRD) experiment shows that the Zn_1‐xCd_xO layers are changed from the single phase of the hexagonal structure at 0≤x ≤0.08 to the double phase of hexagonal‐and‐cubic structure at x =0.13. Thus, the maximum Cd‐composition ratio with the hexagonal structure was found out to be x =0.08. Also, the crystallinity of Zn_1‐xCd_xO layers at x =0.13 was remarkably improved by the RTA annealing treatment. This crystal quality improvement was thought to be associated with the relaxation of the compressive strain remaining in the Zn_1‐xCd_xO layers. Therefore, the results of XRD and transmittance lead that the crystal quality of the Zn_1‐xCd_xO layers forming the hexagonal ZnO phase is better than that forming the cubic CdO phase. Consequently, the reliable formation and the crystallinity of the Zn_1‐xCd_xO layers were achieved by using the RTA method of short‐time thermal‐annealing at the high temperature. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and properties of antimony-doped lanthanum molybdate La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>

Polycrystalline samples of the composition La₂Mo_{2 − x} Sb _x O_{9 − y} , where 0 ≤ x ≤ 0.05, were prepared by solid-phase synthesis. Single crystals of La₂Mo_1.96Sb_0.04O_8.17 were obtained by spontaneous crystallization from flux. The structure of the metastable β _ms phase of this compound was determined at room temperature by X-ray diffraction. It was found that the La, Mo, and O1 atoms are displaced from the threefold axis on which they are located in the high-temperature β phase. It was shown that molybdenum atoms in the crystal structure are partially replaced by antimony atoms, which are located on the threefold axis. In antimony-doped crystals, lanthanum atoms partially return to the site on the threefold axis and the coordination environment of molybdenum cations becomes more ordered, thus facilitating the stabilization of the cubic phase at room temperature. Calorimetric measurements (DSC) showed that the introduction of Sb as the dopant into the La₂Mo₂O₉ structure leads to a decrease in the temperature of the α → β phase transition from 570 to 520°C and to the partial suppression of this transition. The temperature behavior of the conductivity confirms the DSC data. Thus, doping with Sb contributes to the stabilization of the cubic phase at room temperature.     

X‐ray powder diffraction structural characterization of Ba1‐xEuxTiO3 ternary oxides

The single‐phase Ba_1‐xEu_xTiO₃ (0.1≤x≤0.4) samples have been synthesized by solid state reaction under high pressure and ‐temperature. X‐ray powder diffraction data was determined by MS Modeling using Reflex Powder Indexing technique. The Ba_1‐xEu_xTiO₃ series exhibited an interesting orthorhombic‐tetragonal‐cubic structural transformation as Eu composition increases, the distinct change of the X‐ray diffraction peak profile in the vicinity of 45.5º is characteristic of structural transformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase transformation in the system TlBi(Te1‐xSex)2

TlBiTe₂ and TlBiSe₂ ‐ that are ternary analogs of the IV‐VI semiconductors ‐, although they crystallize in the same space group R m (D⁵_3d), exhibit different behaviour during heating. The observed phase transformation depends on Se content (x) in the system TlBi(Te_1‐xSe_x)₂ and the transformation disappears by increasing Se content after a certain value (x = 0.25). This dependence is examined through the analysis of the DSC non‐isothermal measurements and an attempt for the explanation of the observed behaviour is undertaken through the consideration of off‐center atoms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Specific heats of FCC solid solutions of the Bi2O3-Y2O3 system

For the first time specific heats of the face centered cubic solid solutions (Bi₂O₃)_1−x(Y₂O₃)_x in the temperature range 350–1000 K were measured by means of Differential Scanning Calorimetry. Samples were also investigated with thermal expansion. The results showed the phase transitions for (Bi₂O₃)_0.75 (Y₂O₃)_0.25, which is acsribed to δ → δ* change in lattice mentioned in literature and for (Bi₂O₃)_0.58(Y₂O₃)_0.42, which is connected with a metastable behaviour of this sample.     

Synthesis and characterization of compounds LixMn1+xFe2–2xO4 with spinel structure in the quasiternary system “LiO0,5 – MnOx – FeOx“

The thermal decomposition of freeze‐dried Li‐Mn(II)‐Fe(III)‐formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions Li_xMn_1+xFe_2–2xO₄ (0 ≤ x ≤ 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O₂) during the synthesis are required. Because of the high reactivity of the freeze‐dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li‐Mn‐ferrites were studied by chemical analysis, X‐ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A‐sites of the spinel lattice AB₂O₄, while at small x‐values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magneto‐transport properties of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (M = B and Mn)

The magnetic and transport properties of polycrystalline YBa₂ (Cu_1‐xM_x)₃ O_7‐δ (M = B and Mn) superconductor was investigated. Samples of YBa₂(Cu_1‐xB_x)₃O_7‐δ doped with several concentrations of boron B(x = 0.05 and 0.1) were investigated using magnetization measurements. A YBa₂(Cu_1‐xMn_x)₃O_7‐δ sample doped with Mn with concentration of x = 0.02 was investigated using current‐voltage (I‐V) measurements. Our results on the YBa₂(Cu_1‐xB_x)₃O_7‐δ samples reveal a considerable increase in the hysterisis width of the magnetization, M versus the applied magnetic field H with increasing boron concentration. The lower critical field was also found to be enhanced by boron doping. The critical current density, J_c was found to be significantly enhanced in the Mn‐doped sample. The enhancement of J_c was found to be more significant at the lower temperatures for all applied magnetic fields used (0 Oe, 300 Oe, and 500 Oe). Thus, chemical doping is suggested to enhance the vortex pinning forces in the YBCO samples. From the resistivity (R‐T) measurements, chemical doping of the samples was found to have no significant effect on the critical temperature, T_c. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High resolution neutron and X‐ray diffraction studies as a function of temperature and electric field of the ferroelectric phase transition of RDP

Neutron and high resolution X‐ray diffraction investigations on perfect single crystals of RbH₂PO₄ (RDP), a hydrogen bonded ferroelectric of KDP type are reported. The results of crystal structure analysis from diffraction data, below and above the paraelectric ‐ ferroelectric phase transition, support a disorder ‐ order character of [PO₄H₂]^‐‐groups. The tetragonal symmetry of the paraelectric phase with the double well potential of the hydrogen atoms obtained by diffraction, results simply from a time‐space average of orthorhombic symmetry. According to the group ‐ subgroup relation between the tetragonal space group I42d and the orthorhombic Fdd2 a short range order of ferroelectric clusters in the tetragonal phase is observed. With decreasing temperature the ferroelectric clusters increase and the long range interaction between their local polarisation vectors leads to the formation of lamellar ferroelectric domains with alternating polarisation directions at T_C = 147 K. From the high resolution X‐ray data it is concluded that below T_C the ferroelastic strain in the (a,b)‐plane leads to micro‐angle grain boundaries at the domain walls. The tilt angle is enhanced by an applied electric field parallel to the ferroelectric axis. The resulting dislocations at the domain walls persist in the paraelectric phase leading to a memory effect for the arrangement of twin lamellae. With increased electric field the phase transition temperature T_C is decreased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

An optical microscopy study of the biaxial ‐ calamitic nematic lyotropic phase transition

Lyotropic nematic textures are investigated, using optical microscopy, near the reentrant isotropic (I_RE) ‐ discotic nematic (N_D^‐) ‐ biaxial nematic (N_B) ‐ calamitic nematic (N_C⁺) ‐ isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol and D₂O. The N_B, intermediate phase between the two uniaxial nematic ones, is characterized by optical birefringence measurements. In this way, using a polarizing microscope and a colour CCD digital camera, the N_B – N_C⁺ phase transition is identified as well as the domain of the N_B phase and N_D^‐ – N_B transition point in accordance with optical birefringence data (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Specific features of phase transitions and the conduction of La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> oxide-ion conducting compound doped with vanadium

The X-ray powder analysis, calorimetric studies, and conductivity measurements of a series of ceramic La₂Mo_2−x V _x O _y specimens with different vanadium content are performed with the aim of following the dynamics of phase formation of the low-temperature α, high-temperature β, and metastable β _ms phases. At x ≥ 0.06, the cubic phase becomes stable and the monoclinic phase vanishes; therefore, the main α → β transition is suppressed. According to the data of differential thermal analyses, a weak thermal anomaly is observed in the range 450–470°C at x ≥ 0.06. This anomaly is indicative of the β _ms → β transition due to the conversion of the cubic phase with statically disordered oxygen atoms into the cubic phase with dynamic disorder. The conductivity of the high-temperature β phase obeys the Vogel-Tammann-Fulcher law.     

Growth of big single crystals of Sr2YRu1‐xCuxO6 from high temperature solutions

Single crystals of Sr₂YRu_1‐xCu_xO₆ (x = 0 ‐ 0.4) have been grown from PbO‐PbF₂ based solutions in the temperature range 1150 – 1350°C. A silicon carbide heating element furnace (with a recrystallized alumina tube lining) in a vertical configuration was used to grow the crystals in platinum crucibles. Conditions for the stable growth of big crystals have been investigated. The morphology of the crystals containing Cu was found to change from octahedral to cube octahedral as the growth temperature is increased from 1150 to 1350°C. Crystals measuring up to 4.5 mm across and 2.5 mm thick have been grown from 1250°C. The incorporation of Cu into the crystals was ascertained by EDS and x‐ray diffraction analysis. A diamagnetic transition which increased in magnitude and temperature with x was observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The properties of xPbTiO- (0.9 — x) PbZrO- 0.1 PbW0.5Cd0.5O3 solutions in the region of coexistence of tetragonal and rhombohedral phases

The changes of the dielectric permittivity η, dielectric loss tg δ, piezoelectric coefficient d₃₃, pyroelectric coefficient p, remanent polarization P_r and reorientation processes of polarization in dependence on percent content of PbTiO₃ in the xPbTiO₃−(0.9 — x) PbZrO₃− 0.1 PbW_0.5Cd_0.5O₃ solid solutions in the phase coexistence region (PCR) wree investigated. It was pointed out that the characteristics of mentioned parameters possess singularities in this region. The values of average Curie temperature obtained from structural, dielectric and pyroelectric measurements were compared. Presented results let us connect dielectric properties of studied solid solutions with their structure.     

Nonlinear optical properties of strontium tartrato‐antimonate(III) dihydrate,Sr[Sb2{(+)‐C4H2O6}2]·2H2O

The tensor of nonlinear optical susceptibility for second harmonic generation [d^SHG _ijk ] of hexagonal (point group 6) strontium tartrato‐antimonate(III) dihydrate, Sr[Sb₂{(+)‐C₄H₂O₆}₂]·2H₂O, was determined using the Maker fringes method and a Nd:YAG laser with a wavelength of 1064 nm. The largest component of the tensor d^SHG ₃₃₃ amounts two times d^SHG ₁₁₁ of α‐quartz. Effective nonlinear optical susceptibility d^SHG _eff is given for phase matching type I for several wavelengths (for type II d^SHG _eff is nearly zero). The thermal stability of crystals of Sr[Sb₂{(+)‐C₄H₂O₆}₂]·2H₂O was determined in the temperature range from 153 K to 573 K by means of thermal expansion measurements and thermogravimetry. The temperature dependence of thermal expansion coefficients is given in the range from 153 K to 293 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.