Negative Thermal Expansion in the Aluminum and Gallium Phosphate Zeotypes with CHA and AEI Structure types (original) (raw)
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The Journal of Physical Chemistry C, 2017
AlPO 4-17, known as the oxide with the highest negative thermal expansion (NTE), was studied under high pressure by angle-dispersive X-ray diffraction (XRD), mid-and far-infrared (IR) spectroscopy. Upon increasing pressure, the closure of the (P−O−Al) angle destabilizes the porous AlPO 4-17 structure, which drives the amorphization process. On the basis of the decrease in intensity of the XRD lines and broadening of the IR modes, the material was found to begin to amorphize near 1 GPa. XRD, mid-and far-IR analysis evidenced pressure-induced framework softening and complete irreversible amorphization near 2.5 GPa corresponding to the collapse of the pores. The bulk modulus and its first pressure derivative (B 0 = 31.2(5) GPa and B′ 0 = −10.1(3)) at ambient temperature were determined by fitting a third order Birch− Murnaghan equation of state (EOS) to the pressure−volume data. The material is extremely compressible and exhibits an elastic instability. Anomalous (negative) values of B′ 0 are very rare and have been observed previously for cyanides and metal−organic frameworks. Such an instability appears to be characteristic of materials, which exhibit strong NTE behavior and indicates a link between NTE and anomalous compressibility behavior. Mid-IR, far-IR, nuclear magnetic resonance, and pair distribution function analysis of the new amorphous form allow an amorphization mechanism to be proposed corresponding to a collapse of the structure around its pores retaining the columns built up of cancrinite cages and hexagonal prisms, based on alternating AlO 4 and PO 4 tetrahedra. An increase in coordination number of 10% of the Al atoms was observed. The pressure-induced amorphization in the strong NTE material AlPO 4-17 opens the door to the development of new technological applications as crystal−amorphous nanocomposites with zero or specifically selected thermal expansion coefficients.
Materials Science and Engineering: B, 2005
The orthorhombic (␣) low-cristobalite type Al 0.5 Ga 0.5 PO 4 , prepared by co-precipitation followed by high-temperature annealing of the amorphous precipitate has been investigated by powder X-ray diffraction (XRD) at room temperature and variable temperature neutron diffraction technique down to 20 K. In the temperature range of 20-300 K, the crystal structure of this compound has been analyzed by Rietveld refinements of powder neutron diffraction data. This composition crystallizes in the orthorhombic lattice with unit cell parameters: a = 7.030(1), b = 7.015(1), c = 6.923(1)Å and V = 341.4(1)Å 3 (space group C222 1) (at ambient temperature). The unit cell parameters show a gradual decrease with decreasing temperature and the Al 3+ and Ga 3+ ions are statistically distributed over a single crystallographic site forming an ideal solid solution of AlPO 4 and GaPO 4 down to 20 K. The structural details and low-temperature thermal expansion behavior of this compound are reported in this communication. The results are also compared with our earlier thermal expansion studies of cristobalite type phosphates above ambient temperature.
Chemistry of Materials, 2009
Al (1-x) Ga x PO 4 solid solutions (x) 0.14, 0.2, and 0.63) were studied at high temperature up to 1173 K by neutron total scattering. Rietveld refinements confirm the presence of the -quartz-type structure for the lowest Ga content. On the basis of the refinement of the average structure at high temperature, the Al-O and Ga-O distances cannot be distinguished and all intratetrahedral bond distances decrease, which is not reasonable when compared to the thermal expansion behavior of this material. This apparent behavior is due to the presence of a high degree of dynamic disorder at high temperature. In contrast, reverse Monte Carlo (RMC) modeling of neutron total scattering data gives the instantaneous structure in which the two bonds (Al-O) at ∼1.75 Å and (Ga-O) at ∼1.84 Å are partially resolved and increase in length with temperature. The Ga content of the solid solutions is found to modify the structural geometry at high temperature. Increasing the Ga content reduces the Al-O-P angles compared to pure AlPO 4 and lessens their temperature dependence. The results also show that the dynamic disorder in the oxygen sublattice decreases with the Ga-content. As in quartz, the displacive R-phase transition (for x ) 0.14) can be linked to cation displacements as the oxygen sublattice presents a high degree of dynamic disorder well below the transition temperature. The increased temperature stability for Ga-rich compositions can be linked to stronger covalent bonding as is found from the analysis of electron density maps of the pure AlPO 4 and GaPO 4 end members. This approach, based on using chemical substitution to reinforce the covalent nature of chemical bonds, may have implications for improving the thermal stability of a variety of materials used in high-temperature applications.
Comptes Rendus Chimie, 2005
An aluminophosphate with the ERI framework topology, further denoted AlPO-ERI, has been synthesized in the presence of N,N,N′,N′-tetramethyl-1,6-hexanediamine and its structure was solved by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P2(1) (No. 4) with a = 13.163(14) Å, b = 14.793(15) Å, c = 13.215(14) Å, b = 119.74(8)°. As compared to similar materials prepared with piperidine as template, extraframework hydroxyl groups are locally ordered in the structure. After calcination and rehydration, the aluminophosphate remains monoclinic and crystallizes in space group P2(1)/n (No. 14) with a = 13.283(17) Å, b = 14.910(14) Å, c = 22.76(3) Å and b = 90.19(10)°. Both the as made and calcined rehydrated forms of AlPO-ERI have been characterized by multidimensional solid state NMR. AlPO-ERI, isostructural de l'AlPO 4-17, a été préparé en utilisant la N,N,N′,N′-tetramethyl-1,6-hexanediamine comme molécule structurante et sa structure a été résolue sur monocristal. Le solide cristallise dans le groupe d'espace P2(1) (n°. 4) avec a = 13.163(14) Å, b = 14.793(15) Å, c = 13.215(14) Å et b = 119.74(8)°. La symétrie n'est pas hexagonale, comme pour l'AlPO 4-17 préparé en présence de pipéridine, et la structure est localement ordonnée. Après calcination et réhydratation, le solide conserve une symétrie monoclinique et cristallise dans le groupe d'espace P2(1)/n (n°. 14) avec a = 13.283(17) Å, b = 14.910(14) Å, c = 22.76(3) Å et b = 90.19(10). Les solides issus de synthèse, calcinés et réhydratés ont été étudiés par RMN du solide multidimensionnelle.
Polymorph stability and phase transitions of trigonal Al1- x Ga x PO4 mixed crystals
Zeitschrift für Kristallographie - Crystalline Materials, 2001
Single crystals of Al1- x Ga x PO4 of various mole fractions x were grown from phosphoric acid solutions under hydrothermal conditions using the slow-heating method. In order to relate the parameters of this low-quartz structure analogue and the observed phase transitions to the respective mole fraction, the crystals were investigated by means of electron probe microanalysis, X-ray powder diffraction and differential thermal analysis. The results are discussed in terms of the segregation effects occuring during growth. The limiting geometrical parameters for the existence of the high-quartz phase are compared to the values given in the literature.
Journal of Fluorine Chemistry, 2000
The formation mechanisms of microporous materials synthesized under mild hydrothermal conditions are still not elucidated and it is necessary to utilize in situ characterizations for gaining information and new insights concerning the chemical processes which take place within the cell. The hydrothermal crystallizations of the open-framework gallium and aluminium¯uorinated phosphates with the ULM-3 and ULM-4 structural types have been investigated by time-resolved energy-dispersive X-ray diffraction. It has been shown that the nature of the phosphorus source (H 3 PO 4 , polyphosphoric acid or P 2 O 5 ) could drastically affect the crystallization behaviour. For example, in the gallium system, an intermediate appears at short reaction times before the formation of the ULM-3 structure when P 2 O 5 is used instead of H 3 PO 4 , whereas no other phase is observed during the crystallization of ULM-4. However, with aluminium, an intermediate phase is systematically formed before the crystallization of the ULM-3 solid. Kinetics data for each system have been modelled using the Avrami± Erofe'ev equation and these calculations indicate the reactions to be diffusion controlled. #
Powder Diffraction, 2005
The low-cristobalite-type modification of Al 0.5 Ga 0.5 PO 4 is prepared by annealing the amorphous precipitate of stoichiometric phosphate at 1300°C. The phase purity of the sample is ascertained by powder X-ray diffraction. The crystal structure is refined by Rietveld refinements of the neutron and X-ray diffraction data of the polycrystalline powder. This compound crystallizes in an orthorhombic lattice with unit cell parameters, a = 7.0295͑8͒, b = 7.0132͑8͒, and c = 6.9187͑4͒ Å, V = 341.08͑6͒ Å 3 , Z =4 ͑Space group C 222 1 , No. 20͒. The crystal structure analysis reveals the random distribution of the Al 3+ and Ga 3+ having tetrahedral coordination with typical M-O ͑M =Al 3+ :Ga 3+ ͒ bond lengths as 1.74 Å. Similarly, the P 5+ have tetrahedral coordination with typical P-O bond lengths 1.52-1.54 Å. The MO 4 and PO 4 tetraheda are linked by common corners forming a three-dimensional framework lattice. The details of the crystal structure are presented in this paper.
Crystal structure solution and high-temperature thermal expansion in NaZr2(PO4)3-type materials
Acta crystallographica. Section B, Structural science, crystal engineering and materials./Acta crystallographica. Section B, Structural science, crystal engineering and materials, 2024
Á3P 2 O 5)], and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500 C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr 4 P 6 O 24 and CaZr 4 P 6 O 24 was between À1 Â 10 À6 per C and 6 Â 10 À6 per C from 25 to 1500 C. The crystal structures of the high-temperature polymorphs of CaZr 4 P 6 O 24 and SrZr 4 P 6 O 24 with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above $1250 C. This work measured thermal expansion coefficients to 1500 C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.