Download citation
Download citation
link to html
The collected in situ temperature-resolved synchrotron powder data revealed that the transformation of the recently reported three-dimensional τ-Zr(HPO4)2 to cubic ZrP2O7 goes through two intermediate phases. The first intermediate phase, ρ-Zr(HPO4)2, is formed in a reversible phase transition at 598 K, which involves both rearrangement and disordering of the hydrogen phosphate groups of τ-Zr(HPO4)2. At 688 K condensation of the hydrogen phosphate groups leads to the formation of the second intermediate, a new polymorph of zirconium pyrophosphate (β-ZrP2O7). Heating above 973 K results in the gradual transformation of β-ZrP2O7 to cubic zirconium pyrophosphate (α-ZrP2O7). The crystal structures of the two intermediate phases were solved from the in situ powder diffraction data using direct methods and refined using the Rietveld method. Both phases are orthorhombic, space group Pnnm and Z = 2. The lattice parameters for the two phases are: ρ-Zr(HPO4)2: a = 8.1935 (2), b = 7.7090 (2), c = 5.4080 (1) Å; β-ZrP2O7: a = 8.3127 (5), b = 6.6389 (4), c = 5.3407 (3) Å. The formation mechanism for the new zirconium pyrophosphate polymorph, β-ZrP2O7, is discussed in relation to structurally restricted soft chemistry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768100003645/os0045sup1.cif
Contains datablocks tauth_publ, I, II

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768100003645/os0045Isup2.hkl
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768100003645/os0045IIsup3.hkl
Contains datablock II

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768100003645/os0045Isup4.rtv
Contains datablock I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768100003645/os0045IIsup5.rtv
Contains datablock II

Computing details top

For both compounds, program(s) used to refine structure: GSAS.

(I) Zirconium Bis(hydrogenortophosphate) top
Crystal data top
H2O8P2ZrV = 341.59 (2) Å3
Mr = 283.18Z = 2
Orthorhombic, PnnmDx = 2.74 Mg m3
Hall symbol: -P 2 2nSynchrotron radiation, λ = 0.9336 Å
a = 8.1935 (2) ŵ = 1.04 mm1
b = 7.7090 (2) ÅT = 598 K
c = 5.4080 (1) Åwhite
Data collection top
NSLS beamline X7B, BNL
diffractometer
Data collection mode: transmission
Radiation source: X-ray synchrotronScan method: Stationary detector
Specimen mounting: quartz capillary
Refinement top
Refinement on F20 restraints
Rp = 0.031Udef
Rwp = 0.042Weighting scheme based on measured s.u.'s
2142 data points(Δ/σ)max = 0.01
Profile function: pseudo-VoigtBackground function: Chebychev polynomial
57 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Zr0.00.50.00.029 (1)*
P10.3491 (10)0.2442 (11)0.00.040 (2)*.5
P20.2776 (9)0.1612 (9)0.00.027 (2)*.5
O10.3828 (6)0.1475 (7)0.7696 (7)0.043 (2)*
O20.1881 (9)0.3234 (9)0.00.032 (3)*
O30.0170 (3)0.0990 (15)0.50.100 (6)*.5
O40.1479 (12)0.016 (2)0.00.040 (4)*.5
(II) Zirconium Pyrophosphate top
Crystal data top
O7P2ZrV = 294.74 (3) Å3
Mr = 265.16Z = 2
Orthorhombic, PnnmDx = 3.01 Mg m3
Hall symbol: -P 2 2nSynchrotron radiation, λ = 0.9336 Å
a = 8.3127 (4) ŵ = 1.20 mm1
b = 6.6389 (4) ÅT = 778 K
c = 5.3407 (3) Åwhite
Data collection top
NSLS beamline X7B, BNL
diffractometer
Data collection mode: transmission
Radiation source: X-ray synchrotronScan method: Stationary detector
Specimen mounting: quartz capillary
Refinement top
Refinement on F240 parameters
Rp = 0.0290 restraints
Rwp = 0.037Weighting scheme based on measured s.u.'s
1843 data points(Δ/σ)max = 0.01
Profile function: pseudo-VoigtBackground function: Chebychev polynomial
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Zr0.00.50.00.0370 (7)*
P0.3908 (6)0.3129 (7)0.00.047 (2)*
O10.4335 (7)0.2019 (9)0.7710 (11)0.058 (3)*
O20.2222 (14)0.3908 (12)0.00.084 (4)*
O30.00.00.50.107 (5)*
 

Follow Acta Cryst. B
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds