Conformation and Orientation of NO3 in α-Phase Potassium Nitrate

Nimmo, J. K.; Lucas, B. W.

doi:10.1038/physci237061a0

Cited by 8 publications

(8 citation statements)

References 13 publications

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“…The structure of ~-KNOa has been determined by Nimmo & Lucas (1972, and it was shown that the NO3 groups are slightly non-planar [confirmed by Holden & Dickinson (1975)]. This is also the case for both y-and fl-KNOa.…”

Section: Kno3 Phase Transformationsmentioning

confidence: 54%

“…The structure of ~-KNOa has been studied by Edwards (1931) and more recently by Nimmo & Lucas (1972, the latter using single-crystal neutron diffraction data; the Nimmo & Lucas structure has been confirmed by Holden & Dickinson (1975) with single-crystal X-ray data. The unit cell is orthorhombic with a=5.414 (2), b=9.166 (9), c=6.431 (9) A (25°C), Z=4; the space group is Pmcn and the structure is of the aragonite type.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

Nimmo¹,

Lucas²

1976

Acta Crystallogr Sect B

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100

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On heating KNOa at atmospheric pressure, a solid-state phase transformation occurs from e-KNO3 to fl-KNO3 at ,-, 128°C. On cooling from ~200°C, fl-KNO3 transforms at ~ 124°C to y-KNO3, which reverts to e-KNO3 at ,-, 100 °C. The precise temperature range in which the various phases occur depends on the previous treatment of the sample. X-ray powder diffractometer data have been used to determine the structures of y-and fl-KNO3, and the hitherto ambiguous situation concerning the NO3 orientation and disorder has been resolved. For y-KNO3 the space group is R3m with hexagonal axes a= 5.487 (1), c=9.156 (3)A (91°C), Z=3, while for fl-KNO3 the corresponding data are R3m, a=5.425 (1), c= 9-836 (4) ,~ (151 °C), Z= 3. In ~'-KNO3, there are two equivalent types of NOa positions, but within each cell the NO3 groups all belong to one type. With fl-KNO3, each NO3 is in disorder between the two types of position. Relationships between the structures of the e-, B-and y-phases are given. IntroductionAt atmospheric pressure, KNO3 can exist in several different phases depending on the temperature. When heated from room temperature through the transition at ~ 128 °C, KNO3 transforms from an orthorhombic structure (~-KNO3) to a trigonal structure (fl-KNO3). On cooling the fl-phase from ~200°C, KNO3 passes through another trigonal phase (y-KNO3) between ,-~ 124°C and ~ 100°C before reverting to the ~-phase. y-KNO3 exhibits ferroelectric properties (Sawada, Nomura & Fujii, 1958).The structure of ~-KNOa has been studied by Edwards (1931) and more recently by Nimmo & Lucas (1972, the latter using single-crystal neutron diffraction data; the Nimmo & Lucas structure has been confirmed by Holden & Dickinson (1975) with single-crystal X-ray data. The unit cell is orthorhombic with a=5.414 (2), b=9.166 (9), c=6.431 (9) A (25°C), Z=4; the space group is Pmcn and the structure is of the aragonite type. fl-KNOa has been investigated by Tahvonen (1947), Shinnaka (1962) and Stromme (1969), and y-KNO3 by Barth (1939) and Stromme (1969). In these phases, the NO3 conformation and orientation is uncertain. Ordered models have been considered for y-KNOa, static and dynamic disordered models for/3-and y-KNO3, and free rotation models for fl-KNO3. The 7-KNO3 space group has been taken as R3m, but both R3m and R3c have been suggested for fl-KNO3. All fl-and y-KNO3 structural studies have used the X-ray powder diffraction photographic data of Tahvonen (1947) and Barth (1939), respectively. The latter data contained only ten observed reflexions. Shinnaka (1962) also made X-ray diffuse scattering photographic studies.The aim of the present study was to determine the fl-and y-KNO3 structures, and to relate the ~-, fl-and ),-KNO3 structures. Experimental fl-and ~,-KNO3 data were collected on an X-ray powder diffractometer incorporating a small electrical sample furnace. The briquet sample of analytical grade KNO3 was continuously rotated about the diffraction vector. 09--20 scans were made with 3(20)=0.05 ° steps and a step-time of 100 s. Filtered Cu K~ rad...

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Section: Kno3 Phase Transformationsmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 99%

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

Nimmo¹,

Lucas²

1976

Acta Crystallogr Sect B

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100

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“…For α-KNO 3 and γ-KNO 3 , in contrast, K + is coordinated by nine oxygen atoms, and the coordination polyhedra are connected in all three spatial directions by shared corners and edges. [3,4,7,8] In β-KNO 3 -exhibiting disordered NO 3 -anions -the average coordination number is nine, as well. [5][6][7] The observed K-O distances in δ-KNO 3 range from 268.5(2) to 300.3(2) pm and are in accordance to the observed distances in α-KNO 3 , β-KNO 3 , and γ-KNO 3 ( Table 2, Table 3).…”

Section: Dedicated Clustermentioning

confidence: 99%

“…[11] The very next K-O distances are 387.1(2) pm and above, so that the coordination of K + is reliably limited to eight oxygen neighbors. While all oxygen atoms of the nitrate anions are equivalent and coordinated by three K + cations in α-KNO 3 and γ-KNO 3 , [3][4][5][6][7][8] δ-KNO 3 shows a different coordination with oxygen coordinated to two or four K + cations (Figure 4). Thus, two oxygen atoms (O1 and O2) are coordinated by two K + cations, whereas the third oxygen atom (O3) is coordinated by four K + cations.…”

Section: Dedicated Clustermentioning

confidence: 99%

δ‐KNO₃: Synthesis and Structure of a New Modification of Potassium Nitrate

Wolf

Alam

Feldmann

2015

Zeitschrift anorg allge chemie

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Abstract.A novel modification of potassium nitrate is obtained subsequent to solvothermal reaction and crystallization at reduced temperature from diethylformamid (DEF) as solvent. δ-KNO 3 crystallizes with the monoclinic space group P2 1 /c. Most intriguing is the coordination number of potassium and oxygen as expressed by the Niggli notation δ-K 8/8 [NO 4/4 O 4/2 ] that differs from the known modifications of potassium nitrate (α-K 9/9 [NO 9/3 ], β-K 9/9 [NO 9/3 ], γ-K 9/9 [NO 9/3 ]). Moreover,

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“…The crystal structure of α‐KNO 3 has been first described in 1931 by Edwards 3 and has been determined later with high precision using neutron diffraction data by Nimmo and Lucas 1a,4. The β‐phase, with disordered nitrate anions, was frequently characterized, for instance, by Tahvonen in 1947,5 by Shinnaka in 1962,6 as well as by Stromme in 1969 7.…”

Section: Introductionmentioning

confidence: 99%

Zum Zwischenstopp nach Ost‐Frankreich

Irsch¹

2013

Biologie in unserer Zeit

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Conformation and Orientation of NO3 in α-Phase Potassium Nitrate

Cited by 8 publications

References 13 publications

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

δ‐KNO₃: Synthesis and Structure of a New Modification of Potassium Nitrate

Zum Zwischenstopp nach Ost‐Frankreich

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Conformation and Orientation of NO3 in α-Phase Potassium Nitrate

Cited by 8 publications

References 13 publications

The crystal structures of γ- and β-KNO3 and the α ← γ ← β phase transformations

The crystal structures of γ- and β-KNO3 and the α ← γ ← β phase transformations

δ‐KNO3: Synthesis and Structure of a New Modification of Potassium Nitrate

Zum Zwischenstopp nach Ost‐Frankreich

Contact Info

Product

Resources

About

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

The crystal structures of γ- and β-KNO₃ and the α ← γ ← β phase transformations

δ‐KNO₃: Synthesis and Structure of a New Modification of Potassium Nitrate