Synthesis and ultrastructure of plate-like apatite single crystals as a model for tooth enamel

Hydroxyapatite (HAp) is an inorganic constituent compound of human bones and teeth, with superior biocompatibility and bioactivity characteristics. Its crystal structure is hexagonal, characterized by a(b)- and c-planes. In vertebrate long bones, HAp crystals have a c-axis orientation, while in tooth enamel, they have an a(b)-axis orientation. Many methods can be used to synthesize c-axis oriented HAp single crystals; however, to the best of our knowledge, there have been no reports on a synthesis method for a(b)-axis oriented HAp single crystals. In this study, we successfully synthesized plate-like HAp crystals at the air–liquid interface of a starting solution via an enzyme reaction of urea with urease. Crystal phase analysis and ultrastructure observations were carried out, and the results indicated that the particles were single crystals, with almost the same a(b)-axis orientation as tooth enamel. It is hoped that by utilizing their unique surface charge and atomic arrangement, the resulting particles can be used as a high-performance biomaterial, capable of adsorbing bio-related substances and a model for tooth enamel.     

Selective adsorption of acidic protein of bovine serum albumin onto sheet-like calcium hydroxyapatite particles produced by microreactor

The protein adsorption behavior onto sheet-like calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (Hap) particles produced by microreactor was examined by using typical acidic bovine serum albumin (BSA) and basic lysozyme (LSZ). Since the sheet-like Hap particles were highly growth through b- (or a-) and c-axes, the particles had larger fraction of bc (or ac) crystal face. The saturated amounts of adsorbed BSA ($n_s^{\text{BSA}}$) for the sheet-like Hap nanoparticles were increased with increase in the particle size; i.e., $n_s^{\text{BSA}}$ showed a good linear relationship with the total surface area of bc and ac faces of each particle. This result strongly suggested that the sheet-like Hap particles progressed in b- and c-axes with large fraction of C sites on bc and ac particle faces and exhibit a high selective adsorption of BSA. On the contrary, very few LSZ molecules adsorbed onto sheet-like Hap particles. Hence the present study developed that the amounts of adsorbed protein, especially for BSA, can be controlled optimally by altering the size of sheet-like Hap particles. It was also found that the sheet-like Hap particles can be applied to separate completely BSA molecules from BSA–LSZ mixed solution.     

Isovalent Substitution and Heat Treatments Control of T c, Chain Oxygen Disorder and Structural Phase Transition in High T c Superconductors (Y1−x Nd x )SrBaCu3O6+z

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in (Y_1?x Nd _x )SrBaCu₃O_6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] heat treatment increases the orthorhombicity ε=(b?a)/(b+a) (for 0≤x<1), T _c (for x>0.2) and the distance d[Cu(1)–(Sr/Ba)] (decrease T _c) for x<0.25 and decrease it (increase T _c) for x>0.25. When x increase from 0 to 1, ε decreases to 0 with transition from orthorhombic to tetragonal structure. ε[O] decreases with T _c[O]. However, T _c[AO] decreases with ε[AO] until x=0.2, increases for x=0.4 and after it decreases by 9.8 K to 77.2 K for x=1 [AO]. Remarkable correlations were observed between T _c(x) and the volume of the unit cell V(x); and between δT _c(x)=T _c[AO]?T _c[O] and δε(x). A combination of several factors such as decrease in d[Cu(1)–(Sr/Ba)]; increase in cationic and chain oxygen ordering; the number p _sh(x) of holes by Cu(2)–O₂ superconducting plans and in-phase purity for the [AO] samples may account for the observed data.     

Enhanced dielectric constant and structural transformation in Fe-doped hydroxyapatite synthesized by wet chemical method

We report the synthesis of single-phase Fe-doped hydroxyapatite (HAp) [Ca_10?xFe _x (PO₄)₆(OH)₂ (0.0?≤?x?≤?0.3)] and enhanced dielectric constant of HAp with Fe doping. Rietveld analysis shows the change in x-axis-oriented lattice constant a in Fe-doped x?=?0.1 and 0.3 compositions in comparison with parent HAp, while z-axis-oriented lattice constant c does not show any considerable change. Analysis of absorbance data shows two new symmetric stretching peaks for Fe-doped x?=?0.1 and x?=?0.3 compositions, which are not present in parent HAp. Magnetic measurements show paramagnetic behaviour of all Fe-doped samples at 300 K. Fe-doped Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows increase in impedance in the presence of 500 Oersted (Oe) applied magnetic field in comparison with impedance in the absence of magnetic field. Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows increase in dielectric constant in comparison with parent HAp in frequency range 5–35 MHz. Fe-doped Ca_9.9Fe_0.1(PO₄)₆(OH)₂ composition shows?~?970% colossal magnetoimpedance at 100 Hz and?~?200% at 20 MHz frequency.     

Characterization of albumin- and lysozyme–adsorption evaluated on two differently prepared apatites

Ca2+-deficient hydroxyapatite (r-HAp) originated from cattle bones and stoichiometric hydroxyapatite (s-HAp) derived from reagents were prepared by wet syntheses. The adsorption characteristics of albumin (BSA) and lysozyme (LSZ) on the two HAp surfaces were compared by changing the heating temperature of the powders at 273–1073 K in a stream of water vapour. The saturated amount of adsorption (ASA(B) for BSA and ASA(L) for LSZ) on these HAp powders changed little at 273–673 K (Region I), but at 673–1073 K (Region II), clearly increased with crystallite size growth and transformation of crystal morphology. As far as the surface proportions of HAp for P- and C-adsorption sites (the ratios ASA(L)/ASA(B)) are concerned, r-HAp gave no change in Region I and decreased in Region II, whereas those for s-HAp were kept constant through all regions. The heats of LSZ adsorption, QL, for r-HAp and s-HAp, respectively, increased and decreased in Region II. These differences could be a result of the Ca2+-deficient structure of r-HAp with the OH–-vacancy and loosening surface structure due to segregation of impurities in Region II. r-HAp exhibited a 157% higher heat of BSA adsorption, QB, and a 60% lower QL in Region I than s-HAp. Conclusively, r-HAp can be used as an excellent adsorbent, rather than s-HAp, because of its chromatographic characteristics for the separation of acidic and basic proteins. © 1998 Chapman & Hall     

Competitive adsorption of bovine serum albumin and lysozyme on characterized calcium phosphates by polyacrylamide gel electrophoresis method

Characterizations of hydroxyapatite (HA), biphasic calcium phosphate (BCP) and beta tricalcium phosphate (β-TCP) ceramic particles were carried out using X-ray diffusion (XRD), Scanning electron micrograph (SEM), Particle Sizer and Zeta potential analyzer. Competitive adsorption of bovine serum albumin (BSA) and lysozyme (LSZ) on the three calcium phosphates were investigated by polyacrylamide gel electrophoresis (PAGE) method. The results showed that HA, BCP and β-TCP ceramic particles with irregular shapes and similar size distributions all had negative surface net charges in pH7.4 phosphate buffered saline (PBS) solution and exhibited alike behaviors of BSA and LSZ adsorption. LSZ had higher affinity for calcium phosphate ceramics than BSA and its adsorption on them didn’t be almost influenced by the increasing of BSA concentration in the solution. Electrostatic interaction played an important role on the competitive adsorption of BSA and LSZ on the surface of calcium phosphate ceramic particles.     

Crystal structure and thermal annealing behaviors of high d 33 Aurivillius-phase ceramics Li0.04Ce0.04Na(0.46−x/2)Bi(4.46+x/2)Ti(4−x)Sc x O15 with the Sc3+/Bi3+ co-substitution

Modified Aurivillius-type-structured piezoelectric ceramics, Li_0.04Ce_0.04Na_(0.46?x/2)Bi_(4.46+x/2)Ti_(4?x)Sc _x O₁₅ (LiCe–NBT–Sc?x, x = 0, 0.025, 0.075, 0.125, 0.15, 0.175) were synthesized by using conventional solid-state reaction process. Rietveld refinement for the x = 0.125 modified sample was carried out by using powder X-ray diffraction and LiCe–NBT–Sc?0.125 was confirmed to be a four-layer Aurivillius oxide with orthorhombic space group A2 ₁ am [a = 5.45814(7) Å, b = 5.43029(7) Å, c = 40.8547(4) Å and V = 1,210.902(26) Å³; Z = 4], at room temperature. The Sc³⁺/Bi³⁺ substitution led to an increase in Curie temperatures (T _c) and an enhancement in piezoelectric property, and the LiCe–NBT–Sc?0.125 ceramic with a T _c of 675 °C had a high piezoelectric activity (d ₃₃) of 32 pC/N. Variable thermal-annealing d ₃₃ and resistivity (ρ) of the LiCe–NBT–Sc?0.125 ceramic were investigated; the d ₃₃ of the O₂ annealed sample reached up to 37 pC/N, and its resistivity was about 6.8 × 10⁶ Ω cm at 575 °C and about 6.5 × 10⁵ Ω cm at 650 °C.     

Thermal expansion of β-FeSi2 at low temperatures

We present the temperature dependence of the lattice constants (a, b, c) of β-FeSi₂ single crystals at low temperatures. a showed the largest temperature dependence of 0.14% and the relationship of a>c>b did not change at 8-300 K. The linear thermal expansion coefficients α showed remarkable anisotropy. α along the a-axis (αa) was much larger than αb and αc, and showed negative thermal expansion at temperatures below 60 K. From these results, we estimated the temperature dependence of the lattice mismatches at β-FeSi₂/Si heterojunctions.     

An Approach to Use a Raw Single Crystal Whisker as Intrinsic Josephson Junctions Stack

We have developed a technique to observe the intrinsic Josephson effect in Bi₂Sr₂CaCu₂O_8+δ (Bi-2212) single crystal whiskers. In this technique, a raw Bi-2212 single crystal whisker used as intrinsic Josephson junctions (IJJs) along the c-axis. The technique is simple, quick, and less-cost processing. First, a whisker made to stand on ac-plane and then two electrodes were made in ab-planes on either side. The standing whisker with this configuration worked as IJJs. The standing whisker (1.6 mm×40 μm×3 μm) showed the transition temperature of about 84 K. The critical current was about 15 mA at 8 K (critical current density ～23 A/cm²). We observed voltage gap of about 500 mV in current–voltage (I–V) characteristics. This corresponds to a few hundred of IJJs out of ～2,000 IJJs in the whisker thickness. Observations reflect that the technique can be further improved with the single crystal quality, shape of single crystal whisker, and annealing conditions.     

Synthesis,crystal structure,thermal analysis and dielectric properties of two mixed trichlorocadmiates (II)

K_0.57(NH₄) _0.43CdCl₃ and K_0.25(NH₄) _0.75CdCl₃ are orthorhombic, space group Pnma, Z = 4, with a = 8.8760(4) Å, b = 3.9941(2) Å, c = 14.7004(7) Å, and Z = 4, a = 8.9567(9) Å, b = 3.9957(4) Å, c = 14.855 (2) Å, respectively. Final R values are 0.01 and 0.02 for 608 and 834 reflections, respectively. In both the materials, the crystal structure has been determined by X-ray single crystal analysis at room temperature (293 K). The compound structures consist of K⁺ (or NH\(_{{4}}^{{+}})\) cations and double chains of CdCl₆ octahedra sharing one edge extending along b-axis. The mixture of K⁺/NH\(_{{4}}^{{+}}\) cations are located between the double chains ensuring the stability of the structure by ionic and hydrogen bonding contacts N/K–H …Cl. Spectroscopic, dielectric and differential scanning calorimetry (DSC) measurements were performed to discuss the mechanism of the phase transition. These studies show that these materials, K_0.57(NH₄)_0.43CdCl₃and K_0.25(NH₄)_0.75CdCl₃, undergo a phase transition at 438 and 454 K, respectively.     

Falkner–Skan flows past moving boundaries: an exactly solvable case

The Falkner–Skan flows past stretching boundaries are revisited in this paper. The usual assumption U _w (x) = λ U(x), i.e. the proportionality of the stretching velocity U _w (x) and the free stream velocity U(x) is adopted. For the special case of a converging channel (wedge nozzle), U(x) ~ ? 1/x, exact analytical solutions in terms of elementary hyperbolic functions are reported. In the range ? 2 < λ < + 1 dual solutions describing either opposing (λ < 0) or aiding (λ > 0) flow regimes were found. In the range λ > 1 unique solutions occur, while below the critical value λ _c  = ? 2 no solutions exist at all. The mechanical features of these solutions are discussed in some detail.     

On the crystal chemistry of hollandite-like phases with TlV5S8 structure: The crystal structures of TlxTi5S8, TlxV5S8 and TlCr5S8

The title compounds are monoclinic, space group C2/m, Z = 2 with the lattice constants (in Å): a = 17.859, b = 3.433, c = 8.804, β = 104.26° (Tl_xTi₅S₈)a = 17.490, b = 3.297, c = 8.511, β = 103.95° (Tl_xV₅S₈)a = 17.767, b = 3.431, c = 8.594, β = 104.68° (TlCr₅S₈) The crystal structures of Tl_xTi₅S₈ and Tl_xV₅S₈ were refined from single crystal data (R = 4.3% and 3.7% respectively), and the centrosymmetry of the TlV₅S₈ type was proven.     

High-pressure Synthesis and Physical Characterization of Y-based 1222-type Niobio–Cuprate NbSr2(Y1.5Ce0.5)Cu2O10

We have successfully synthesized a new 1222-type Y-based niobio-cuprate for the first time with the chemical composition, NbSr₂(Y_1.5Ce_0.5)Cu₂O₁₀ by a high-pressure and high-temperature (HPHT) technique under different synthesis conditions. Good quality (nearly single-phase) Nb1222Y polycrystalline sample was synthesized at 1,450^?○C and 6 GPa for 2 h. It crystallizes in a tetragonal symmetry of space group I4/mmm with lattice parameters a=b=3.863(2) Å and c=28.687(5) Å, which is isostructural with the corresponding Ru1222Y (RuSr₂(Y_1.5Ce_0.5)Cu₂O₁₀) phase. The dc-magnetic susceptibility measurements show a mixed magnetic state at ～29 K, which is apparently associated with magneto-superconductivity. The magnetic moment (M) versus field (H) curve of Nb1222Y sample measured at 1.8 K looks like a hybrid and it normally ensembles for both superconducting and a ferromagnetic curve. As the field increases, a low field diamagnetic signal emerges. However, temperature dependence of electrical resistivity of Nb1222Y did not show superconductivity, but semiconducting nature with a relatively large magnetoresistance (～6% at almost entire region). No specific heat anomaly was observed at the vicinity of the transition temperature.     

The framework topology of magnesiumaluminophosphate structure type 36

The crystal structure of MAPO-36 was solved and refined by combining information obtained bysynchrotron powder, Weissenberg single crystal (of an imperfect crystal), and electron and GuinierLenné powder diffraction. The powder pattern was indexed using a monoclinic cell (C2/c) with a = 13.148, b = 21.577, and c = 5.164 Å and β = 91.84°. Powder patterns were calculated for hypothetical models having similar cell parameters and a match was finally achieved for a model related to but topologically different from cancrinite. The aluminophosphate-based molecular sieve structure type 36 is based on the 4.6.12 two-dimensional net (gml) and the double zigzag chain (zz), but unlike cancrinite, it has both radial and tangential chains around the 12-ring. This gives an elliptical channel with staggered annular side pockets. Even though it has smaller channels, these side pockets give it a greater adsorption capacity than that of AIPO-5.     

Interplay Between Diamagnetic and Ferromagnetic Phase in (Bi2223)1−y (LSMO) y Composites Thick Films

Thick films of ((Bi,Pb)₂Sr₂Ca₂Cu₃O _x )_1?y (La_0.7Sr_0.3MnO₃) _y [(Bi2223)_1?y (LSMO) _y ] composites (y=0.01, 0.03, 0.05) are deposited by means of a simple melting-quenching-annealing method onto (001)-oriented LaAlO₃(LAO) substrates. The constituent compounds Bi2223 and LSMO are prepared by standard solid-state reaction and sol–gel method, respectively. Measurements of the dependence of the magnetization on the temperature show the presence of superconducting and ferromagnetic phase below ～54 K and ～370 K, respectively. Current–voltage measurements on composites with y=0.01, 0.03 show that the superconducting critical current drop dramatically from I _c≈350 mA at T=15 K to zero at T≈0.5T _c (～25 K). The dependence of the magnetization on the external magnetic field applied in-plane or out-of-plane at 5 K displays well defined hysteresis loops, which correspond to the superconducting, diamagnetic phase. For T>T _c, the ferromagnetic loop of LSMO is observed. The critical current density, J _c, was determined for samples with y=0.01 and 0.05 by applying Kim’s model to the superconducting, diamagnetic hysteresis recorded at 5 K. The calculated values for J _c(B) resulted to be smaller than those obtained for individual bulk Bi2223 samples due, probably, to the presence of LSMO particles whose ferromagnetic domains compete with the superconducting diamagnetic phase.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

Mixed-Cation Thallium Phosphates Containing Di-, Tri-, and Pentavalent Cations

The mixed phosphates TlMn²⁺P₃O₉(a= 9.422 Å, b= 7.3199 Å, c= 12.227 Å sp. gr. Pnma), TlGaHP₃O₁₀(a= 12.01 Å, b= 8.471 Å, c= 9.098 Å, = 111.98° sp. gr. C2/c), and TlTa(PO₄)₂(a= 5.0308 Å, c= 8.497 Å sp. gr. P321) were obtained by precipitation from polyphosphoric-acid melts containing di-, tri-, and pentavalent cations in combination with Tl⁺. The crystal structures of TlMn²⁺P₃O₉and TlTa(PO₄)₂were determined by single-crystal x-ray diffraction.     

Microstructure of a-plane ZnO grown on LaAlO3 (001)

The microstructure of a-plane ZnO grown on LaAlO₃ (LAO) (001) has been systematically investigated by employing X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Based on the results of XRD and TEM, only a-plane ZnO has been found to grow on LAO (001), and it consists of two types of domains perpendicular to each other. The crystal orientation relationships of a-plane ZnO domains with LAO have been verified to be [0001]_ZnO//[110]_LAO and [11?00]_ZnO//[11?0]_LAO. The domain boundaries in the a-plane ZnO are along the direction in a rotation angle of about 45° from the c-axes of ZnO. The surface morphology of ZnO films in SEM exhibits domain structure in stripe-like shape. The formation of two domains can be attributed to the cubic symmetry of the surface configuration of LAO (001).     

Crystal and molecular structure of adducts of uranyl pivaloyltrifluoroacetonate with hexamethylphosphoramide and of uranyl trifluoroacetylacetonate with trimethyl phosphate

Crystal and molecular structures of adducts of uranyl pivaloyltrifluoroacetonate with hexamethylphosphoramide [UO₂(PTFA)₂(HMPA)] (I) and of uranyl trifluoroacetylacetonate with trimethyl phosphate [UO₂(TFA)₂(TMP)] (II) were determined. Compound I crystallizes in the monoclinic system, space group P2₁/n; a = 16.9384(3), b = 9.1090(2), c = 20.9844(4) Å, β = 101.5337(10)°, V = 3172.34(11) ų (at 100 K); Z = 4. Compound II crystallizes in the rhombic system, space group Pbca; a = 17.8214(4), b = 7.7786(2), c = 30.9176(7) Å, V = 4285.97(18) ų (at 100 K); Z = 8. In both cases, the cis isomer in which the neutral ligand is located between the trifluoromethyl groups is realized. Compound I differing from II by the stronger branching of ligand periphery is characterized by stronger structural deformations in the crystal.     

Hybrid open-frameworks: hydrothermal synthesis,structure determinations and magnetic properties of MIL-29, two copper diphosphonates (CuII(H2O))2{O3P–X–PO3} with X=C2H4, CH2–C6H4–CH2

Two copper diphosphonates were hydrothermally synthesized using ethylenediphosphonic and p-xylenediphosphonic acids, synthesized according the Arbuzov method. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–CH₂–PO₃} already described from powder data, was solved from single crystal data. Its symmetry is monoclinic (space group P2₁/c (no. 14)) with lattice parameters a=8.0670(4) Å, b=7.5889(4) Å, c=7.3997(4) Å, β=116.281(2)°, V=406.18(4) ų, Z=2. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–(C₆H₄)–CH₂–PO₃} was solved by powder X-ray diffraction (space group P2₁/c (no. 14)) with lattice parameters a=10.812(1) Å, b=7.577(1) Å, c=7.412(1) Å, β=92.34(1)°, V=606.7(2) ų, Z=2. Both structures are built up from identical inorganic layers covalently linked by the organic chains which act as pillars. The inorganic layers contain dimers of edge-sharing CuO₄(H₂O) square pyramids linked by the PO₃C tetrahedra. Both compounds are antiferromagnetic at 4(1) K.