Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

Belik, Alexei А.; Izumi, Fujio; Ikeda, Takuji; Lazoryak, Bogdan I.; Морозов, В.А.; Малахо, А. П.; Stefanovich, S. Yu.; Гребенев, В. В.; Shelmenkova, Oksana V.; Kamiyama, Takashi; Oikawa, Kenichi; Леонидов, И. А.; Леонидова, О. Н.; Давыдов, С. А.

doi:10.1080/10426500212245

Cited by 12 publications

(6 citation statements)

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“…Ca 3 - x Sr x (PO 4 ) 2 was also studied by different authors. , Britvin et al described a mineral strontiowhitlockite, Sr 9 Mg(PO 3 OH)(PO 4 ) 6 , which is an Sr derivative of synthetic whitlockite, Ca 18 Mg 2 H 2 (PO 4 ) 14 and a solid-state method. − …”

Section: Introductionmentioning

confidence: 99%

Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

et al. 2002

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Solid solutions Ca 3-x Sr x (PO 4 ) 2 (0 e x e 16/7) were studied by X-ray powder diffraction, infrared spectroscopy, differential scanning calorimetry, electrical-conductivity measurements, and second-harmonic generation. Phosphates with 0 e x e 12/7 ( -phase) crystallize in space group R3c, Z ) 21, a ≈ 10 Å, and c ≈ 38 Å. Sr-rich phosphates with 13/7 e x e 16/7 ( ′-phase) have a somewhat different crystal structure: space group R3 hm, Z ) 10.5, a ≈ 10 Å, and c ≈ 19 Å. The solid solutions with 0 e x e 12/7 showed a reversible high-temperature phase transition a ′, where the and ′ phases have noncentrosymmetric and centosymmetric structures, respectively. The temperature of the phase transition decreased with increasing Sr content. In Ca 3 (PO 4 ) 2 , a new phase transition, a ′, was observed at 920°C in the electrical-conductivity measurements. The structure parameters of polar -Ca 2 Sr(PO 4 ) 2 (x ) 1) and centrosymmetric ′-Ca 5/7 Sr 16/7 (PO 4 ) 2 (x ) 16/7) at room temperature were refined by Rietveld refinements of the X-ray diffraction data: space group R3c, Z ) 21, a ) 10.5612(2) Å, and c ) 38.0588 (5) Å for -Ca 2 Sr(PO 4 ) 2 and space group R3 hm, Z ) 10.5, a ) 10.7015(2) Å, and c ) 19.5787(2) Å for ′-Ca 5/7 Sr 16/7 (PO 4 ) 2 . -Ca 2 Sr(PO 4 ) 2 is isotypic with -Ca 3 (PO 4 ) 2 . In -Ca 2 Sr(PO 4 ) 2 , the M4 site is 50% occupied by Sr 2+ ions, and the M6 site is vacant. In both structures, Ca 2+ and Sr 2+ ions enter the M1-M3 sites whereas Ca 2+ ions selectively occupy the M5 site. ′-Ca 5/7 Sr 16/7 (PO 4 ) 2 contains some disordered atoms: (1) cations at the M3 site are statistically distributed among several positions near the center of symmetry, (2) P1O 4 tetrahedra are orientationally disordered, and (3) the M4 site (M6 site in -Ca 2 Sr(PO 4 ) 2 ) is occupied by 0.165Sr 2+ + 0.085Ca 2+ + 0.750. The mechanism of the a ′ phase transition in Ca 3-x Sr x (PO 4 ) 2 (0 e x e 12/7) is discussed on the basis of the crystal data.

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Section: Introductionmentioning

confidence: 99%

Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

et al. 2002

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“…In Ca 9 R(VO 4 ) 7 (R = Y and Tb−Lu), the stress at the M5 site is relieved by the partial occupation by Ca 2+ ions. Note that phosphates Sr 9 R(PO 4 ) 7 could be prepared for R = Y and Gd−Lu. , However, Sr 9 R(PO 4 ) 7 (R = Y and Tb−Lu) exhibits a monoclinically distorted β-Ca 3 (PO 4 ) 2 -type structure (space group I 2/ a ), , whereas Sr 9 R(VO 4 ) 7 (R = Tm, Yb, and Lu) are isotypic with Ca 3 (VO 4 ) 2 (and β-Ca 3 (PO 4 ) 2 ) having space group R 3 c . We may also expect the formation of solid solutions of Sr 9- y Ca y R(VO 4 ) 7 (R = Tm, Yb, and Lu) for 0 ≤ y ≤ 9 because the boundary compositions are isotypic with each other …”

Section: Resultsmentioning

confidence: 99%

“…Solid solutions of Ca 3- x Sr x (VO 4 ) 2 with the structure of Ca 3 (VO 4 ) 2 are formed in the compositional range of 0 ≤ x ≤ 1.5, while solid solutions of Ca 3- x Sr x (PO 4 ) 2 with the β-Ca 3 (PO 4 ) 2 -type structure have a longer extension with 0 ≤ x ≤ 2.31 . Strontium phosphates with the β-Ca 3 (PO 4 ) 2 -related structures can be stabilized by different cations, e.g., Sr 9 R(PO 4 ) 7 (R = Sc, Cr, Fe, Ga, Y, In, and Gd−Lu), , Sr 9.3 Ni 1.2 (PO 4 ) 7 , Sr 9 NiLi(PO 4 ) 7 , Sr 9.04 Ni 1.02 Na 0.88 (PO 4 ) 7 , and Sr 9.04 Ni 1.04 K 0.76 (PO 4 ) 7 . Note that Sr 9.04 Ni 1.02 Na 0.88 (PO 4 ) 7 and Sr 9.04 Ni 1.04 K 0.76 (PO 4 ) 7 (space group R 3 c and Z = 6) are isotypic with β-Ca 3 (PO 4 ) 2 …”

Section: Introductionmentioning

confidence: 99%

New Noncentrosymmetric Vanadates Sr₉R(VO₄)₇ (R = Tm, Yb, and Lu): Synthesis, Structure Analysis, and Characterization

et al. 2004

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New vanadates Sr9R(VO4)7 (R = Tm, Yb, and Lu) were synthesized using a standard solid-state method at 1373 K and found to be isotypic with Ca3(VO4)2 at room temperature (RT). Their structure parameters were refined using the Rietveld method from synchrotron X-ray diffraction (XRD) data measured at RT (space group R3c and Z = 6). Sr9R(VO4)7 (R = Y and La−Er) do not form a phase isotypic with Ca3(VO4)2. Sr9R(VO4)7 (R = Tm, Yb, and Lu) were characterized through the magnetic susceptibility (2−400 K), the specific heat (0.45−31 K), thermal analysis (300−1573 K), and high-temperature XRD, second-harmonic generation, and dielectric measurements. The temperature dependence of the dielectric constant and tangent loss suggested that they exhibit a reversible ferroelectric−paraelectric phase transition of the first order near 950−960 K. The high-temperature phases have space group R3̄m and Z = 3. Thermal analysis revealed the presence of an intermediate phase between the R3c and R3̄m phases in a very narrow temperature range. Magnetic susceptibilities of Sr9Tm(VO4)7 and Sr9Yb(VO4)7 are typical of Tm3+ and Yb3+ ions affected by an octahedral crystal field. The effective magnetic moments were 7.39 μB for Tm3+ and 4.59 μB for Yb3+.

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“…This original technique of structure refinement has successfully been applied to several inorganic materials: the positionaldisorderofK + ionsinterlayeredinK x Ti 2-x/3 Li x/3 O 4 , 4,6 atomic arrangements of K clusters in a K-type zeolite Linde Type A, 7 the nuclear/electron-density distribution in a high-T c superconductor HgBa 2 CuO 4+δ , 4,8 the ab initio structure analysis of a helix-layered silicate, 9 and conduction pathways in a high ionic conductor Rb 4 Cu 16 I 7.2 Cl 12.8 . 10 Belik et al [11][12][13] have recently reported that strontium phosphates Sr 9+x M 1.5-x (PO 4 ) 7 (M ) Mn, Fe, Co, Ni, Cu, and Cd) that are structurally similar to β-Ca 3 (PO 4 ) 2 contain highly disordered atoms. Structure parameters of Sr 9 Fe 1.5 (PO 4 ) 7 12 and Sr 9.1 Cu 1.4 (PO 4 ) 7 13 were refined from XRD data by using space group R3 hm (a ≈ 10.6 Å and c ≈ 19.7 Å).…”

Section: Introductionmentioning

confidence: 99%

“…Belik et al − have recently reported that strontium phosphates Sr 9+ x M 1.5 - x (PO 4 ) 7 (M = Mn, Fe, Co, Ni, Cu, and Cd) that are structurally similar to β-Ca 3 (PO 4 ) 2 contain highly disordered atoms. Structure parameters of Sr 9 Fe 1.5 (PO 4 ) 7 12 and Sr 9.1 Cu 1.4 (PO 4 ) 7 13 were refined from XRD data by using space group R 3̄ m ( a ≈ 10.6 Å and c ≈ 19.7 Å).…”

Section: Introductionmentioning

confidence: 99%

Positional and Orientational Disorder in a Solid Solution of Sr₉₊_xNi_1.5_-_x(PO₄)₇ (x = 0.3)

et al. 2002

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Solid solutions of Sr 9+x Ni 1.5-x (PO 4 ) 7 that are structurally related to β-Ca 3 (PO 4 ) 2 are formed in the compositional range of 0.14 e x e 0.39. We investigated static disorder in Sr 9.3 Ni 1.2 -(PO 4 ) 7 (x ) 0.3, space group: R3 hm) by X-ray and neutron powder diffraction. The electrondensity distribution in Sr 9.3 Ni 1.2 (PO 4 ) 7 was determined by Rietveld refinement and subsequent whole-pattern fitting based on the maximum entropy method (MEM) from synchrotron X-ray powder diffraction data measured at 100 K. The resulting electron densities served to derive an expedient split-atom model. By adopting this model, we refined the structure parameters of Sr 9.3 Ni 1.2 (PO 4 ) 7 by the Rietveld method from the X-ray diffraction data as well as from time-of-flight neutron powder diffraction data measured at 293 K. The Rietveld refinement with the X-ray diffraction data gave R wp ) 5.39% and R B ) 2.80%. Further MEM-based pattern fitting appreciably decreased the R factors to R wp ) 5.18% and R B ) 1.03%, which demonstrates that the highly disordered structure of Sr 9.3 Ni 1.2 (PO 4 ) 7 can be expressed more accurately with electron densities than with structure parameters. The asymmetric unit of Sr 9.3 Ni 1.2 (PO 4 ) 7 contains two Sr sites (Sr1 and Sr3), one Ni site (Ni5), one mixed-metal site (M4), two P sites (P1 and P2), and five O sites. Sr3 atoms are statistically distributed among four positions near the center of symmetry. Sr 2+ and Ni 2+ ions are split to occupy the M4 site that is 75% vacant. P1O 4 tetrahedra are orientationally disordered.

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Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

Cited by 12 publications

References 4 publications

Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

New Noncentrosymmetric Vanadates Sr₉R(VO₄)₇ (R = Tm, Yb, and Lu): Synthesis, Structure Analysis, and Characterization

Positional and Orientational Disorder in a Solid Solution of Sr₉₊_xNi_1.5_-_x(PO₄)₇ (x = 0.3)

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Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

Cited by 12 publications

References 4 publications

Polar and Centrosymmetric Phases in Solid Solutions Ca3-xSrx(PO4)2 (0 ⩽ x ⩽ 16/7)

Polar and Centrosymmetric Phases in Solid Solutions Ca3-xSrx(PO4)2 (0 ⩽ x ⩽ 16/7)

New Noncentrosymmetric Vanadates Sr9R(VO4)7 (R = Tm, Yb, and Lu): Synthesis, Structure Analysis, and Characterization

Positional and Orientational Disorder in a Solid Solution of Sr9+xNi1.5-x(PO4)7 (x = 0.3)

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Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

Polar and Centrosymmetric Phases in Solid Solutions Ca₃_-_xSr_x(PO₄)₂ (0 ⩽ x ⩽ 16/7)

New Noncentrosymmetric Vanadates Sr₉R(VO₄)₇ (R = Tm, Yb, and Lu): Synthesis, Structure Analysis, and Characterization

Positional and Orientational Disorder in a Solid Solution of Sr₉₊_xNi_1.5_-_x(PO₄)₇ (x = 0.3)