In the last decade, most publications on the mechanical properties of dental calcified tissues were based on nanoindentation investigation. This technique has allowed a better understanding of the mechanical behavior of enamel, dentin, and cementum at a nanoscale. The indentations are normally carried out using pointed or spherical indenters. Hardness and elastic modulus are measured as a function of indenter penetration depth and from the elastic recovery upon unloading. The unique microstructure of each calcified tissue significantly contributes to the variations in the mechanical properties measured. As complex hydrated biological composites, the relative proportions of the composite components, namely, inorganic material (hydroxyapatite), organic material, and water, determines the mechanical properties of the dental hard tissues. Many pathological conditions affecting dental hard tissues cause changes in mineral levels, crystalline structures, and mechanical properties that may be probed by nanoindentation. This review focuses on relevant nanoindentation techniques and their applications to enamel, dentin, and cementum investigations.

Nanoindentation: Application to dental hard tissue investigations

Synthesis and characterization of nanocrystalline gallium nitride by nitridation of Ga-EDTA complex

The structural, mechanical and transport properties of RuSr2GdCu2O8 sintered between 1000 and 1065 ◦ Ci n O 2 atmosphere have been studied by XRD, microhardness and Seebeck coefficient measurements. The pellets have a tetragonal perovskite-type structure. Microhardness and bulk density of the considered samples increase with increasing sintering temperature. TEP is positive for all samples and decreases with increasing sintering temperature. The normal state TEP data are discussed in view of some theoretical models, namely a two-band model with an additional linear T term and variable range hopping models. (Some figures in this article are in colour only in the electronic version)

Influence of sintering temperature on thermopower and hardness of RuSr2GdCu2O8

The nitridation reaction is significantly important to utilize the unique properties of nitrides and nitrogen-doped materials. However, nitridation generally requires a high temperature or highly reactive reagents (often explosive) because the energies of N–N bond cleavage and nitrogen anion formation (N3–) are very high. We demonstrate the first room-temperature synthesis of GaN directly from GaCl3 by nanoscale atom exchange reaction. Nonequilibrium nitrogen molecules with very high translational energy were used as a chemically stable and safe nitrogen source. The irradiation of molecular nitrogen to the desired reaction area successfully provided a gallium nitride (GaN) nanosheet that exhibited a typical photoluminescence spectrum. Because this process retains the target substrate room temperature and does not involve any photon nor charged ion, it allows damage-less synthesis of the semiconducting metal nitrides, even directly on plastic substrates such as polyethylene terephthalate (PET).

Room-Temperature Synthesis of GaN Driven by Kinetic Energy beyond the Limit of Thermodynamics.

We report structural, electrical, thermopower and magnetic properties of the Ru1?xCoxSr2Eu1.5Ce0.5Cu2O10?? (1.0?x?0.0) system. Substitution of Co at the Ru?site in the Ru1?xCoxSr2Eu1.5Ce0.5Cu2O10?? system takes place iso-structurally in the tetragonal structure (space group I4/mmm) with full solubility (x = 1.0). Superconductivity (SC) exists for x up to x = 0.075 only and at higher Co concentrations SC is totally suppressed. The magnetic behaviour of the materials with Co up to x = 0.2 preserves the magnetic structure of the parent RuSr2Eu1.5Ce0.5Cu2O10?? compound. For 0.8?x?0.2 an antiferromagnetic-like transition is seen at TN = 31?K, which remains invariant regardless of the Co content. CoSr2Eu1.5Ce0.5Cu2O10?? (x = 1) seems to be an itinerant magnet, which orders magnetically at around 110?K, though for such an assertion further work is warranted. In general, the magnetization measurements as such did not reveal the complete information on the magnetic structure and hence the neutron scattering measurements are still required to resolve the complex magnetism of Ru1?xCoxSr2Eu1.5Ce0.5Cu2O10?? and even the pristine system.

http://iopscience.iop.org/article/10.1088/0953-8984/19/2/026203/pdf

Experimental study of magneto-superconductor RuSr2Eu1.5Ce0.5Cu2O10- δ : peculiar effect of Co doping on complex magnetism and Tc variation

Samples of Ru(1-x)Co(x)Sr(2)GdCu(2)O(8) (x = 0, 0.01, 0.03, and 0.05) were synthesized by solid-state reaction. X-ray diffraction data indicate that all the samples are single phases with Ru-1212 structure. Rietveld refinement was carried out to determine the structure parameters. We present an investigation of the dc magnetic properties. The remnant magnetization at 5 K increases with the increasing of Co content, and the ferromagnetic ordering temperatures are slightly decreased with Co content increase. Substitution of Ru with Co suppresses superconductivity strikingly. The suppression of superconductivity is related to increasing ferromagnetic component in the RuO(2) layers by Co doping and the decrease of the average (Ru,Co)-O bond length of (Ru,CO)O(6) octahedra. (C) 2003 Elsevier B.V. All rights reserved.

Effect of Co substitution on superconductivity and magnetic order in RuSr2GdCu2O8

Gallium nitride (GaN) has been synthesized by reacting gallium trichloride with ammonia (NH(3)) at low temperatures ranging from 500 to 1000 degreesC for 12 h. X-ray diffraction, transmission electron microscopy, infrared, and Raman backscattering spectra revealed that the synthesized GaN powder consists of single-phase nano-sized crystallites with the wurtzite-type structure. The average size of the crystals decreases with the reaction temperature from approximately similar to63 nm at 1000 degreesC to similar to5 nm at 500 degreesC. GaOCl and epsilon-Ga(2)O(3) are the intermediate products during synthesis of the GaN. Characteristic shifts of the Raman peaks are associated with the change in crystal size. The band-edge emission of GaN at 361 nm was observed on room temperature photoluminescence spectra exclusively for the sample synthesized at 1000 degreesC, while a new and broad emission band appeared with the center ranging from 827 to 765 nm for the samples synthesized between 500 and 800 degreesC.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400087525

Low-temperature synthesis and characterization of GaN nanocrystals from gallium trichloride precursor

The crystal structures of a series of new compounds with the composition FeSr(2)LnCu(2)O(7+delta) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb) that were successfully synthesized by solid-state reaction are investigated. The Rietveld refinement of the X-ray diffraction data shows that the samples exhibit a transition from a tetragonal system with space group P4/mmm for light rare earths Ln = La, Nd, Sm, Eu, and Gd to an orthorhombic system with space group Pmmm for heavy rare earths Ln = Dy, Ho, Er, and Yb. The oxygen contents of the samples are chemically determined by the iodometric titration. The room-temperature Mossbauer spectroscopy of (57)Fe in FeSr(2)GdCu(2)O(7+delta) is used to study the site distribution of Fe between the 1a and 2g sites in the as-synthesized in the air samples and O(2)-annealed samples, respectively. In the as-synthesized sample, there are about 67% of Fe ions residing in the la site, whereas in the 02-annealed sample, there are about 61% of Fe ions residing on the la site. Magnetization measurements indicate that Z changes with temperature in a Curie-type manner. Resistance measurements indicate that these samples have a semiconductor-like behavior and their band gap is related to their structural type and the radius of rare earth ions.

Systematic study on crystal structure and properties of FeSr(2)LnCu(2)O(7+delta) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb)

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Effect of Co substitution on superconductivity and magnetic order in RuSr2GdCu2O8

Low-temperature synthesis and characterization of GaN nanocrystals from gallium trichloride precursor

Systematic study on crystal structure and properties of FeSr(2)LnCu(2)O(7+delta) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb)