The low-temperature phase of sodium azide

Aghdaee, S.R.; Rae, A. I. M.

doi:10.1107/s0108768184002007

Cited by 18 publications

(11 citation statements)

References 8 publications

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“…[12][13][14] Metal azides undergo a variety of pressure or temperatureinduced phase transitions, a phenomenon which has been intensively studied. [14][15][16][17][18][19][20][21][22][23][24][25] The behavior of the azide anions (N 3 À ) during the phase transition is noticeable. In the temperatureinduced tetragonal-cubic phase transitions of both rubidium azide (RbN 3 ) and cesium azide (CsN 3 ), a fluctuation of the orientation of N 3 À anions was observed.…”

Section: Introductionmentioning

confidence: 99%

Phase transition and structure of silver azide at high pressure

Hou

Zhang

et al. 2011

Journal of Applied Physics

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Abstractilver azide (AgN 3 ) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters aand b, a 3° rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be inI4/mcm space group, with Ag at 4a, N 1 at 4d, and N 2 at 8h Wyckoff positions. Both of the two phases have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be K OT = 39 ± 5 GPa with K OT ' = 10 ± 7 and K OT = 57 ± 2 GPa with K OT ' = 6.6 ± 0.2, respectively. KeywordsMechanical Engineering, Materials Science and Engineering, High pressure, Phase transitions, Active galaxies, Silver, Equations of state, X-ray diffraction, Polymers, Anisotropy, Elastic moduli, Magmatic magnetic minerals Disciplines Aerospace Engineering | Materials Science and Engineering | Mechanical Engineering CommentsThe following article appeared in Journal of Applied Physics 110 (2011) Silver azide (AgN 3 ) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters a and b, a 3 rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be in I4/mcm space group, with Ag at 4a, N 1 at 4d, and N 2 at 8h Wyckoff positions. Both of the two phases have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be K OT ¼ 39 6 5 GPa with K OT ' ¼ 10 6 7 and K OT ¼ 57 6 2 GPa with K OT ' ¼ 6.6 6 0.2, respectively.

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Section: Introductionmentioning

confidence: 99%

Phase transition and structure of silver azide at high pressure

Hou

Zhang

et al. 2011

Journal of Applied Physics

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“…1). The structure of the α-form was later confirmed by a combination of X-ray single-crystal and powder diffraction [12].…”

Section: Introductionmentioning

confidence: 91%

“…At the same time, Hirotsu's study of the birefringence of a single crystal also gave clear evidence for a first order transition [20]. These contemporaneous results had a significant impact on opinion in the literature -subsequent observations have been contextualised using models that emphasise the displacive nature of the transition [21][22][23][24] Careful measurements of the unit cell parameters and symmetry-breaking shear strains as a function of temperature between 12 and 295 K confirmed that the transition involves a coupling of the canting of the azide anion (order-disorder) with the shearing of the sodium layers (displacive) [12]. This is illustrated in Fig.…”

Section: Introductionmentioning

confidence: 91%

Structural characterization of sodium azide and sodium bifluoride at high pressures

Millar

Barry

Marshall

et al. 2014

Zeitschrift Für Kristallographie Crystalline Materials

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This paper reports the structural characterization of sodium azide and sodium bifluoride (hydrogenfluoride) at elevated pressures using neutron powder diffraction. Compression of sodium azide at 294 K induces a transition from the β-phase to the α-phase. This structure responds to increasing pressure by progressive tilting of the azide groups. Compression of the α-form to 3.33 GPa at 393 K results in a phase transition to the tetragonal γ-phase (space group I4/mcm), which is isostructural with the azides of the heavier Group 1 elements and features square-antiprism co-ordination of the cations. On decompression at ambient temperature, the γ-phase reverts to the α-phase, but with substantial peak broadening indicative of significant strain within the recovered sample. Compression of sodium bifluoride (NaDF 2 -I to 0.66 GPa at ambient temperature resulted in the formation of NaDF 2 -II, which adopts an orthorhombic, marcasite-like (space group Pnnm) structure. Further compression to 4.58 GPa resulted in a transition to NaDF 2 -III, which adopts the archetypal I4/mcm structure shared by the heavier alkali metal bifluorides and γ-NaN 3 .

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“…The crystallographic structures of both forms of NaN 3 have been determined through use of both x-ray and neutron diffraction, [8] and they are related in such a way that a continuous interchange between the structures is possible and the heatcapacity curve near the transition is -type. Of four studies that have investigated the nature of the transition, one [9] called it second order, another [10] called it weakly first order, and two [11,12] called it predominantly second order. Three reports [13][14][15] for ⌬ t H gave values varying between ∼0.01 and ∼0.1 kJ/mol, but these indications that ⌬ t H 0 were apparently based on the integration of heat-capacity curves and may be indicative of the energy of randomization that is distributed over a temperature range preceding the transition and thus are not a valid proof of a first-order transition.…”

Section: Complicationsmentioning

confidence: 99%

Crystallography and phase equilibria a review: Part III—Second-order transitions and approximations

Smith

2005

J Phs Eqil and Diff

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Fig. III-2Comparison of Gibbs energy differences, G-G°versus , where G is the Gibbs energy of the low-symmetry structure and G°i s the Gibbs energy of the high-symmetry structure. (a) For a first-order transition: the upper curve for T > T t shows the low-temperature form to be metastable and the high-temperature form to be stable; the middle curve for T = T t shows the two forms to exist in equilibrium; and the lower curve for T < T t shows the high-temperature form to be metastable and the low-temperature form to be stable. (b) The situation for a second-order transition: the upper curve shows that for T ‫ס‬ T t and for T > T t there is a single structure; at T < T t a double-valued curve develops with minima values of increasing and of G-G°becoming more negative with decreasing temperature. of the double-valued curve defines a single symmetry independently of the + or − sign (see text).

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The low-temperature phase of sodium azide

Cited by 18 publications

References 8 publications

Phase transition and structure of silver azide at high pressure

Phase transition and structure of silver azide at high pressure

Structural characterization of sodium azide and sodium bifluoride at high pressures

Crystallography and phase equilibria a review: Part III—Second-order transitions and approximations

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