Triple phosphates of calcium, sodium and trivalent elements with whitlockite-like structure

Chemical Department, Moscow State University, 119899, GSP, Moscow, Russia
Materials Research Bulletin (Impact Factor: 1.97). 02/1996; 31(2):207-216. DOI: 10.1016/0025-5408(95)00181-6

ABSTRACT Triple phosphates of calcium, sodium and trivalent elements (Eu, Nd, Fe) in Ca3(PO4)2-RPO4-Na3PO4 systems were predicted on the basis of crystal chemistry data and synthesized. The obtained phases were studied by XRD, IR-spectroscopy and emission spectroscopy under 90Sr-90Y and λ = 380 nm excitation. The only phosphates with the whitlockite-like structure appear within the range of Ca3(PO4)2-Ca9Na1.5R0.5(PO4)7-Ca10Na(PO4)7 compositi The emission spectra of phases with europium under 90Sr-90Y excitation consist of transition lines in Eu3+ and two broad bands of inherent luminescence of the matrix with maximums at ~ 360 and ~ 510 nm.

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    ABSTRACT: We have prepared Ca9.5 − x Pbx M(PO4)7 (M = Mg, Zn, Cd) and Ca10.5 − x Pbx (PO4)7 solid solutions. A polar whitlockite-like (sp. gr. R3c) crystal structure exists in the range 0 ≤ x ≤ 1.5 for all of the M cations in Ca9.5 − x Pbx M(PO4)7 and in the range 0 ≤ x ≤ 2.5 for Ca10.5 − x Pbx (PO4)7. X-ray powder diffraction profile analysis results for Ca8.5PbCd(PO4)7 powder demonstrate that the small divalent M cations reside predominantly on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located primarily on the M4 site. Differential scanning calorimetry, second-harmonic generation, and dielectric permittivity data indicate that all of the synthesized phosphates are high-temperature ferroelectrics. The highest Curie temperatures are offered by the x = 0.5 materials, in which most of the lead resides in the spacious oxygen polyhedra M4 and only a small amount of lead is incorporated into the smaller polyhedra around M1–M3. The nonlinear optical activity has a maximum in the middle of the solid-solution series and is an order of magnitude higher than that of the parent, lead-free phases.
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    ABSTRACT: In the hard oxidizing fire iron red glaze which colorated red exposed magnesioferrite and whitlockite-type crystals. And whitlockite-type crystals has formed before magnesioferrite forming in the step of sintering. This study tries to identify the coloration mechanism of hard oxidizing fire iron red glaze by the experiment of substitution of whitlockite-like crystals and to confirm such substitution be able to farm magnesioferrite. As the results of experiment, magnesioferrite was appeared during substitution of two kinds of whitlockite-type. It can be considered that the magnesioferrite colors the iron glaze to red with covering the glaze surface.
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    ABSTRACT: The structural properties, X-ray-excited radioluminescence and thermally stimulated luminescence (TSL) of Ca9Ln(PO4)7 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were investigated. (La–Nd) occupied mainly the largest M3 site, whereas the smallest lanthanides (Yb, Lu) adopted the smallest octahedral M5 site. The intermediate-sized ions (Sm–Tm) occupied the medium-sized sites M1 and M2. Only the Ln3+ ions with the highest Ln3+/4+ ionization energy (Ln = Pr, Nd, Tb, Dy) were able to trap holes and become luminescent centers for thermally stimulated Ln3+ 4f–4f emission. For low Ln3+/4+ ionization potential (Ln = La, Gd, Yb, Lu), no hole trapping at Ln3+ was possible and Mn2+ impurities at the M5 sites were the effective hole traps and luminescent centers for thermally stimulated Mn2+ 3d–3d red emission. Very broad TSL peaks were attributed to thermally assisted detrapping of electrons from positive traps, possibly Ln3+ at Ca2+ sites, tunneling back towards the hole trap/luminescent center. Ca9Ln(PO4)7 compounds doped with Ln = Tb or Lu were found to be efficient X-ray-excited long-lasting phosphorescence materials, emitting in the green and in the red, respectively.
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