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)     

Crystal growth of PZN‐PT single crystals and critical issues for higher piezoelectric coefficient

Single crystals of lead zinc niobate‐lead titanate (1‐x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ for x = 8% and 9% have been grown by flux method using Lead Oxide (PbO) as flux. Low scan rate XRD has been carried out to investigate on the structural influence of the compositional variations in the grown crystals. Transmission spectra in the range of UV‐Vis‐Near IR and mid IR regions have been carried out to understand the distortions caused in the BO₆ octahedral lattice. Morphological aspects of as‐grown PZN‐PT crystals have also been investigated. Dielectric measurements clearly explained the dependence of T_c and diffusiveness with PT content. The values of P_r and E_cobtained from P‐E loops suggest the presence of ordered domain state in these PZN‐PT single crystals. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of TGS and DTGS single crystals doped with Pt(II), Pt(IV) and L‐alanine

The single crystals of triglycine sulfate doped with bivalent and tetravalent Pt‐ions and with L‐alanine (LADTGS/Pt(II) and LATGS/Pt(IV)) were grown in the ferroelectric phase from low temperature solutions. Using stick seeds the full‐shaped crystals with many growth pyramids have been prepared. The growth rate along the axis c of the doped crystals is much higher than in an undoped one. Morphology, domain structure and P‐E hysteresis loops have been investigated. The effect of the dopant on the growth velocity is explained on the basis of catalytic action of supposed platinum complexes. The first series of the pyroelectric detectors have been prepared from these materials and their fundamental parameters are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An effective growth method to improve the homogeneity of relaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3‐ Pb(Mg1/3Nb2/3)O3‐PbTiO3

Compositional segregation usually has negative effects on the growth of solid solution ferroelectric single crystals of Pb(In_1/2Nb_1/2)O₃‐Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (abbr. PIN‐PMN‐PT or PIMNT). A modified Bridgman method was adopted in this work to control the segregation and improve the compositional homogeneity significantly. The characteristic of this work is to use multiround growths and gradient composition raw materials in order to keep the PbTiO₃ concentration constant during the crystal growth. As an example, the two‐round growth of ternary PIN‐PMN‐PT single crystal is conducted in the same Pt crucible with gradient raw materials, where the first‐round boule was used as the seed crystal for the second‐round growth. Our results show that the as‐grown (Ф80 mm × 270 mm) PIN‐PMN‐PT crystals exhibit higher phase transition temperatures (T_c∼180 °C, T_r/t∼110 °C) and larger coercive field (E_c∼5–5.5 kV/cm), which are much better than the performances of Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ crystals, and similar dielectric and piezoelectric performances (ε∼5000, tanδ∼1.25%, d₃₃∼1500 pC/N, k_t∼60%). And about 85 percent of the crystal boule grown by the two‐round growth technique could maintain its compositions around the morphotropic phase boundary.     

Optical properties of pure and metal ions doped ammonium sulfate single crystals

A study of the optical properties of pure‐and some metal ions doped ammonium sulfate crystals (AS) were made. Optical constants of AS crystals were calculated at room temperature. The optical absorption coefficient (α ) was analyzed and interpreted to be in the allowed direct transition. The introduction of Rb⁺ or Cs⁺ ions gives rise to an intense charge transfer band with a maximum at λ= 310 nm in the optical spectrum. In case of Cr³⁺ ‐doping, the absorption shows a shoulder just before the onset band to band transition. The values of the allowed direct energy gap E_g for undoped and doped crystals were calculated. It was found that E_g values were decreased with metal ions doping. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were calculated as a function of photon energy. The validity of Cauchy‐Sellimeier equation was checked in the wavelength range 4.9 ‐ 5.6 eV and its parameters were calculated. Applying the Single‐Effective‐Oscillator model, the moments of ε (E ) could be estimated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of large‐sized Nd:YAG single crystals grown by horizontal directional solidification

Nd³⁺‐doped Y₃Al₅O₁₂ single crystals have been grown by the horizontal directional solidification (HDS) method in different thermal zone. The Grashof (G_r), Prandtl (P_r), Marangoni (M_a) and Rayleigh (R_a) numbers of melt in HDS system have been discussed for our experimental system to understand the mechanism of melt flow patterns and concentration gradient of dopant. The concentration gradient of Nd³⁺ ions was explained with melt flow processes during crystal growth in different thermal zone, and results indicated that high growth temperature will be helpful for uniformity of dopant in HDS‐grown single crystal. The main microscopic growth defects such as bubbles and irregular inclusions in HDS‐grown Nd:YAG crystals were observed, and the causes were discussed as well. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Kinetics of etching of dislocations in magnesium orthosilicate single crystals

Cleavages of undoped, doped and natural magnesium orthosilicate crystals have been simultaneously etched in concentrated hydrochloric acid solution. The lateral and normal velocities of the growth of pits were then measured at different temperatures for the varieties of crystals. The time dependence of the growth of pit dimensions is found to be linear, while the temperature dependence of the growth of pits is found to be exponential, viz. V = A exp (− E/kT). The dissolution parameters, e. g. the activation energy (E) and the pre-exponential factor (A) for dissolution along the surface and along the dislocation lines have been computed. It is observed that: (1) the activation energy (E₁) of dissolution along [001] direction is found to be greater than the activation energy (E_b) along [100] direction, irrespective of whether the crystals are doped, undoped or natural, and (2) the doping of the crystal with manganese has lowered down the activation energy (E_d) to such an extent that it is less than E₁ and E_b. The implications are discussed.     

Growth,Structural and Microtopographical Studies of Calcium Iodate,Monohydrate Crystals Grown in Silica Gel

Single crystals of calcium iodate, monohydrate [Ca(IO₃)₂, H₂O] have been grown by gel technique. Prismatic, prismatic pyramidal, needle shaped and hopper crystals were obtained. These crystals were also grown by doping impurities such as copper and iron. Kinetics of growth parameters was investigated. Structural analysis was carried out by using X‐ray powder diffraction method. Microtopographical study of the habit faces, such as prismatic and pyramidal, of as grown crystals was carried out. Some surface structures are reported. These crystals were etched by various etchants and appropriate etchant is reported.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Crystal structure,dielectric properties of (K0.5Na0.5)NbO3 single crystal grown by flux method using B2O3 flux

Lead free piezoelectric single crystals of sodium potassium niobate (K_0.5Na_0.5)NbO₃ (KNN) were grown by high‐temperature solution method using two different fluxes; one with a mixture of NaF and KF and other with addition of B₂O₃ along with the mixture. In the present study, the growth of KNN crystals without B₂O₃ flux and the same with B₂O₃ flux were compared. It was found that additions of small amounts of B₂O₃ lowered the melting temperature of the solid solution and enabled better dielectric properties. Phase analysis showed that all samples were crystallized in pure orthorhombic perovskite phase. AFM morphological studies showed that the addition of B₂O₃ flux increased the roughness of the grown crystal. Further, addition of B₂O₃ flux slightly decreased the orthorhombic to tetragonal phase transition temperature T_(O—T) and the Curie temperature T_C. The ferroelectric behaviour of KNN single crystal has been investigated at room temperature. The crystal grown using B₂O₃ flux exhibited a remanent polarization (P_r) ∼ 32 μC/cm² and coercive field (Ec) of ∼11.8 kV/cm whereas the crystal grown without the use of B₂O₃ flux had a remanent polarization (P_r) ∼ 36 μC/cm² and coercive field (Ec) of ∼14.6 kV/cm.     

Thermal and electrical properties of Tri Glycine Sulpho Phosphate (TGSP) and L‐Asparagine doped TGSP crystals

Tri Glycinsulphate with partial substitution of phosphoric acid, namely Tri Glycine Sulpho Phosphate (TGSP) has been grown by slow cooling method. Habit modifications have been observed with change in the concentration of ortho phosphoric acid (H₃PO₄). Monoclinic structure of the grown crystals has been confirmed using X‐ray diffraction analysis. TGSP crystals doped with L – Asparagine were also grown. The doping effect is qualitatively estimated using FTIR analysis. TGA, DTA studies and dielectric measurements were carried out for pure and L‐Asparagine doped TGSP crystals to investigate the thermal and electrical properties of the crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of near‐stoichiometric LiNbO3 crystals and Li2O contents determination

Two kinds of near‐stoichiometric LiNbO₃ crystals (SLN11 and SLN19) were grown by a flux pulling method from stoichiometric melt with addition of 11mol%K₂O and 19mol%K₂O, respectively. Compared with the congruent melting LiNbO₃, the ultraviolet absorption edges of two crystals shift towards shorter wavelengths, and the locations of the OH^‐ infrared absorption band have obvious change and the bandwidths become greatly narrower. From these experimental results, the Li₂O contents are determined indirectly to be about 49.6mol% for SLN11 and 49.9mol% for SLN19, respectively. The Li₂O content in SLN19 is very close to the ideal value of 50mol%. The coercive fields of two crystals were measured by the poling method at room temperature. A linear relationship between the Li₂O content and the coercive field was fitted. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Real Structure of LiB3O5 (LBO) Crystals Grown in Li2O‐B2O3‐MoO3 System

The liquidus surface structure and field of LiB₃O₅ (LBO) primary crystallization have been revealed in Li₂O‐B₂O₃ ‐MoO₃ ternary system. The optimization of charge composition and growth conditions results in large volume optical quality LBO single crystals yielding. Crystallographic properties and real defect structure of grown LBO single crystals have been investigated by X‐ray powder diffraction method and X‐ray reflection topography. The volume of the crystals is partly free of any structural imperfections.     

Growth of ytterbium tartrate trihydrate crystals in silica and agar‐agar gels and their characterization

Single crystals of ytterbium tartrate trihydrate have been grown by gel method using silica and agar‐agar gels as media of growth. The medium of growth influences the morphology of grown crystals, silica gel yielding single and polycrystalline in the form of spherulites whereas agar‐agar gel leading to growth of single and twinned crystals. Materials grown as single crystals have been characterized by using optical and scanning electron microscopy (SEM), EDAX, XRD, FT‐IR, CHN and thermogravimetric techniques. The stoichiometry of the grown single crystals is suggested to be Yb(C₄H₄O₆) (C₄H₅O₆).3H₂O. The FT‐IR spectrum shows the presence of singly as well as doubly ionized tartrate ligands. Results of thermal analysis indicate that the material is thermally stable up to a temperature of 200 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Energetic Band Location of Rhenium-doped MoSe2 Single Crystals to Assess their Usefulness in PEC Solar Cell Fabrication

Single crystals of MoSe₂ and rhenium-doped MoSe₂ have been grown by direct vapour transport technique and characterized by optical and electrochemical studies. The transmission spectra show the crystals of MoSe₂ and rhenium-doped MoSe₂ to be direct band gap semiconductors with band gap 1.6 eV and 1.2 eV, respectively. Mott-Schottky plots have been drawn to determine the type of semiconductor and its parameters, N_d, E_C and E_V.     

Thermodynamic Analysis of Urea Physical Vapour Transport

The vaporisation-condensation scheme of urea has been investigated in the temperature region below the melting point, in order to establish the thermodynamic reactions on which the physical vapour transport (PVT) of urea is based. By making use of both reported data and experimental results of MS, DTA, DTG, and HPLC analysis, it was shown that PVT relevant reactions are basically molecular sublimation and partial decomposition in solid biuret and ammonia. MS analysis of urea crystals and source residues have also shown that no decomposition can be observed in the growing crystals, unless reheated during growth. The temperature dependence of the decomposition pressure has been found to be: log₁₀P_NH3 [torr] = 38 – 13840/T [K]. The use of this relation in diffusive mass transport calculations brought to linear growth rate values not in disagreement with the experimental values found in closed tube PVT grown crystals.     

Structure and optical properties of near stoichiometric Ce:LiNbO3 crystals

The near sotichiometric Ce:LiNbO₃ (Ce:SLN) crystals were grown by the top seeded solution growth (TSSG) method by adding K₂O flux to Li₂O‐Nb₂O₅ melt. Their UV‐vis absorption spectra and IR spectra were measured and discussed to investigate their defect structure. The results showed that the grown crystals were near stoichiometric and Ce ions in the crystals located the Li site. Photorefractive properties of Ce:SLN crystals were studied by two‐wave coupling experiment. The results of the two‐wave coupling experiments of the crystals showed that as the CeO₂ doping concentrations increased, the diffraction efficiency increased, photoconductivity decreased and the writing time and erasure time increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of axial vibration on Bi12SiO20 crystal growth by vertical Bridgman technique

Bi₁₂SiO₂₀ single crystals have been grown successfully by vertical Bridgman technique. During the crystal growth process, different axial vibration amplitudes of 50 μm, 70 μm and 100 μm were applied with the same vibration frequency of 50 Hz. The effect of different axial vibration amplitudes on quality of the as‐grown Bi₁₂SiO₂₀ single crystals was discussed. The crystals have been characterized by X‐ray rocking curve optical and absorption spectrum. The experimental results reveal that the axial vibration amplitude has a pronounced effect on quality of the as‐grown Bi₁₂SiO₂₀ single crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the study of elastic properties of KGd(WO4)2:Er3+ single crystals by Brillouin spectroscopy

In this paper we present the study of the acoustic phonons propagating in Er³⁺‐doped KGd(WO₄)₂ single crystals by Brillouin spectroscopy. For the investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101] and [110] have been determined. Moreover, the values of the elastic constants: C₂₂, C₄₄ and C₆₆ of Er³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Er³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% does not influence their elastic properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spherulitic crystallization of β‐In2Te3 by physical vapour deposition

Different morphologies of indium telluride (In₂Te₃) including novel spherulites were crystallized using the physical vapour deposition (PVD) method, by varying the difference in the growth and source zone temperature (ΔT) of a dual zone horizontal furnace assembled indigenously. Whiskers and kinked needles of In₂Te₃were grown at ΔT = 250 K and 300 K respectively, maintaining the growth zone at 500 °C. At high supersaturation (Δ T = 400 K), spherulitic crystals were obtained. The stoichiometric composition of these crystals has been confirmed using energy dispersive analysis by x‐rays (EDAX). The structure of β‐In₂Te₃ spherulitic crystals is identified as zinc blende with lattice parameter a = 6.159 Å, from x‐ray diffraction (XRD) studies. The scanning electron microscope (SEM) images revealed the radial structure of the grown spherulites. The growth mechanism for the spherulitic crystallization of β‐In₂Te₃ crystals has been discussed based on the theoretical models. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)