The space group and structure of α-K<sub>2</sub>SO<sub>4</sub>

Berg, A. J. van den; Tuinstra, F.

doi:10.1107/s0567740878010432

Cited by 55 publications

(12 citation statements)

References 6 publications

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“…The expansion for co consists of 2 linear portions, one below and the other above 350 ~ After By and large, this thermal expansion behaviour of K2CrO 4 appears similar to that of K2SO 4, but there is a significant difference in the expansions of a o and b o. Whereas in ~-K2S04, a 0 and b 0 expand in the same proportion (tl'ie straight lines are nearly parallel) [3], here we found that b 0 alone is expanding faster and the bo/V-3 values near the transition temperature continuously approach the values of a H. It is probable that the high order-disorder kind of transition found in K2S04 [4] may be less in this case. However, an accurate redetermination of the thermal expansion of K2SO 4 and an accurate structure analysis of K2CrO 4 in both the low-and the high-temperature form is essential for a critical assessment of the above conclusion.…”

Section: Resultscontrasting

confidence: 46%

Thermal expansion and crystallographic phase transformation in K2CrO4

Amirthalingam

1984

Journal of Thermal Analysis

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The unit cell parameters of potassium chromate were determined between 56 and 880~ from high temperature X-ray powder data and the thermal expansion parameters were derived. These were compared with those of potassium sulphate.As a continuation of earlier studies on the nature of the phase transformations in Na2CrO4 [1], work on the thermal expansion and phase transformation in anhydrous K2CrO 4 is reported. It is known that K2CrO4, which has a ~-K2SO 4 type structure at room temperature (space group Pmcn), assumes a hexagonal structure of Na2SO 4 (1) type when heated above 663 ~ [2]. Accurate cell data and X-ray powder data at room temperature and 705 ~ are available in ASTM 15-365 and 15-359. The results obtained now are compared with those on K2SO 4 to determine the extent of similarity between them. ExperimentalThe experimental technique used was the same as that described earlier [1]. X-ray powder patterns at 56, 154, 257, 358, 446, 640, 705, 738, 850 and 888 ~ were recorded. (The temperature measurements have an error of about 1-3 deg.) The d values obtained have been least square fitted to arrive at the lattice parameters of the orthorhombic and hexagonal forms at these temperatures and are plotted with their ESD's ( Fig. 1). At high temperatures the ESD's are larger because of the weakening of some of the X-ray reflections and a consequent reduction in the number of observables used in the least square process. Results and discussionAs seen in Fig. 1, the thermal expansions for ao and bo/V-3 are linear. The expansion for co consists of 2 linear portions, one below and the other above 350 ~ After

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Section: Resultscontrasting

confidence: 46%

Thermal expansion and crystallographic phase transformation in K2CrO4

Amirthalingam

1984

Journal of Thermal Analysis

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“…Below T c = 223 K, they undergo a ferroelectric phase transition (PT) without a change in the number of formula units per unit cell into the space group P n2a 1 [1,2]. This PT is accompanied by a significant step in the strain, while the spontaneous polarization P c below T c decreases in magnitude and changes its sign near 85 K [3].…”

Section: Introductionmentioning

confidence: 99%

“…The unit cell of AS crystals contains four formula units, which possess two nonequivalent ammonium ions NH (2) and SO 4 groups. It has been concluded that SO 4 tetrahedra in the paraelectric phase do not have two equilibrium positions and move in a single-minimum potential [7,8].…”

Section: Introductionmentioning

confidence: 99%

Baric Shift of Phase Transition in Ammonium Sulfate Crystals

Gaba

2010

Acta Phys. Pol. A

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The influence of uniaxial mechanical pressures (σ m ≤ 200 bar) on the spectral (300-800 nm) and temperature (77-300 K) dependences of the refractive indices n i , the birefringence ∆n i and the phase transition point in ammonium sulfate crystals are studied. It is established that the uniaxial pressure does not change character of the dispersion dn i / dλ, but only its value λ The shift of the phase transition in ammonium sulfate under the uniaxial mechanical pressure is analyzed.

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“…Crystals of solid solutions of Cs x (NH 4 ) 1-x LiSO 4 belong to the family of double sulfates with general formula being ALiSO 4 , where: A = (Cs, NH 4 , Rb, K, Na). The crystalline structure of these compounds may be considered as a small distortion of the prototype structure a-K 2 SO 4 with P6 3 / mmc symmetry [1]. For majority of compounds, this phase is not observed experimentally.…”

Section: Introductionmentioning

confidence: 99%

“…Values of parameters T o , T p , and T e of the solid solution of Cs 0.90 (NH 4 ) 0.10 LiSO 4 for thermal anomaly(1) …”

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confidence: 99%

Detection of a ferroelastic phase transition in Csx(NH4)1−xLiSO4 with the use of the DSC method

Czaja

2013

J Therm Anal Calorim

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In this paper the technology of producing solid solutions of Cs x (NH 4 ) 1-x LiSO 4 using the slow evaporation method is presented. Appropriate conditions were chosen to grow large samples. The ammonium ion content in the solid solutions was determined using the Kjeldahl method. It was found that the real ammonium ion concentration is twice lower than the one applied in the initial substances. At room temperature, the base crystal, lithium cesium sulfate (CsLiSO 4 ), is paraelastic, whereas lithium ammonium sulfate (NH 4 LiSO 4 ) is ferroelectric. It is expected that as a result of substituting Cs ? ions with NH þ 4 ions, instead of the Cs ? ions, the modification of the ferroic properties of solid solutions of Cs x (NH 4 ) 1-x LiSO 4 will take place. Tests conducted with the use of the differential scanning calorimetry method (DSC) allowed the detection of the ferroelastic phase transition which takes place in these compounds. A gradual increase of temperature transition was observed from 202 K for the pure CsLiSO 4 to 203.8 K for Cs 0.90 (NH 4 ) 0.10 LiSO 4 and 230.1 K for Cs 0.85 (NH 4 ) 0.15 LiSO 4 with the increase of NH þ 4 ions concentration. Using polarized light microscopy, a ferroelastic domain structure was detected in the examined solid solutions, which appeared below the structural phase transition temperature.

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The space group and structure of α-K₂SO₄

Cited by 55 publications

References 6 publications

Thermal expansion and crystallographic phase transformation in K2CrO4

Thermal expansion and crystallographic phase transformation in K2CrO4

Baric Shift of Phase Transition in Ammonium Sulfate Crystals

Detection of a ferroelastic phase transition in Csx(NH4)1−xLiSO4 with the use of the DSC method

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The space group and structure of α-K2SO4

Cited by 55 publications

References 6 publications

Thermal expansion and crystallographic phase transformation in K2CrO4

Thermal expansion and crystallographic phase transformation in K2CrO4

Baric Shift of Phase Transition in Ammonium Sulfate Crystals

Detection of a ferroelastic phase transition in Csx(NH4)1−xLiSO4 with the use of the DSC method

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The space group and structure of α-K₂SO₄