Incommensurate cooperative tilting modes of MnF<sub>6</sub>octahedra relatedto the structural phasetransitions in BaMnF<sub>4</sub>

Hidaka, M.; Yoshimura, M.; Nishimori, Hidetoshi; Fujii, H.; Park, Yong Jun; Park, Jae Hyun; Lee, Ki Bong

doi:10.1080/01411590108224556

Cited by 5 publications

(3 citation statements)

References 17 publications

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“…The superspace group (SSG) was taken from a study of comparable n = 4 materials (e.g., Sr 2 Nb 2 O 7 ) where there is a similar modulation observed in the a axis. [1,2] Although these n = 4 analogs have a modulation vector of q ≈ (0.5, 0, 0) and is similar to the doubling of the a axis in BaMnF 4 (A2 1 am space group setting), reported by Hidaka; [21] it is important to note that due to the alternate space group setting the incommensuration in BaMnF 4 lies along the polar axis, but in the n = 4 oxides the incommensuration is orthogonal to the polarization. Given the similarities between the reported modulations in A 2 B 2 O 7 ferroelectrics and the candidate modulation vectors determined from TEM here, a modulation vector of approximately q = (0.5, 0, 0) was used as an initial value in refinements of data at 483 K. This resulted in a final value of q = (0.456, 0, 0) for LaTaO 4 at 483 K. Refining the PND data using the Cmc2 1 (α00)0s0 SSG, with a maximum satellite index of 3, gave a satisfactory fit of all reflections, with an overall χ 2 = 2.57 (R wp = 5.6%) across two HRPD detector banks ( Figure 5).…”

Section: Determination Of Macroscopic Modulationsupporting

confidence: 69%

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Howieson

Gibbs

et al. 2020

Adv Funct Materials

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The layered perovskite LaTaO 4 has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate-commensurate first-order transition between incommensurate Cmc2 1 (α00)0s0 and commensurate Cmc2 1 orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)-roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at T IC-C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.

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Section: Determination Of Macroscopic Modulationsupporting

confidence: 69%

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Howieson

Gibbs

et al. 2020

Adv Funct Materials

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“…The unit-cell volumes of the individual BaMF 4 compounds are linearly correlated with the ionic radius of the M 2+ ion 1 . Earlier low temperature investigations have shown that BaMnF 4 , which is the compound with the largest M 2+ ion, undergoes a phase transition to an incommensurate phase at T = 245 K and atmospheric pressure [19,23,25,26]. Diffraction studies on other members of the family (M = Mg, Zn) do not provide any evidence of phase transitions down to 10 K [23].…”

Section: Introductionmentioning

confidence: 90%

Structural stability of BaMF₄(M = Mg, Zn and Mn) at high pressures

Posse

Friese

Grzechnik

2011

J. Phys.: Condens. Matter

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Piezoelectric fluorides of the composition BaMF(4) (M = Mg, Zn, Mn) have been studied in situ at high pressures in diamond anvil cells with single-crystal x-ray diffraction and Raman spectroscopy. All three compounds crystallize in the acentric space group Cmc 2(1) at ambient pressure. BaMgF(4) undergoes a reversible second order phase transition to the paraelectric phase (space group Cmcm) at pressures between 5 and 6 GPa. BaZnF(4) undergoes a reversible first order phase transition to a monoclinic phase (space group P 11n). Both high- and low-pressure polymorphs coexist in the pressure range 5-7 GPa. BaMnF(4) maintains the Cmc 2(1) structure up to pressures of 4 GPa. Above this pressure the diffraction signal decreases rapidly and at 6 GPa no diffraction signal could be detected in our experiment. The compound does not recover its crystallinity on decompression. A comparison of the effects of external and chemical pressure is presented.

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“…It was concluded that the BaMF 4 compounds are structurally unstable at low temperatures. Until now, this instability has only been confirmed for BaMnF 4 , which transforms to an incommensurately modulated phase at temperatures below 250 K described by Sciau et al (1988), Scott (1979), Hidaka et al (2001) and Yoshimura & Hidaka (2005).…”

Section: Introductionmentioning

confidence: 98%

Ternary fluorides BaMF₄ (M = Zn, Mg and Mn) at low temperatures

Posse¹,

Grzechnik²,

Friese³

2009

Acta Crystallogr Sect B

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Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10 K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250 K. The modulated phase is stable down to 10 K. The magnetic anomalies at 45 and 27 K observed previously in BaMnF4 are exclusively reflected in the behavior of the gamma component of the q vector, which assumes an irrational value of approximately 0.395 A(-1) at the temperature corresponding to the onset of the magnetic ordering and then stays constant down to 10 K. Mn-Mn distances do not indicate any structural response to the magnetic ordering. The formation of the modulated phase can be explained on the basis of simple geometrical criteria. The incorporation of the large Mn cation in the octahedral sheets implies an increase of the cavity in which the Ba ion is incorporated. This leads to the formation of the modulated structure to adapt the coordination sphere around Ba in such a way that the bond-valence sums can be kept close to the ideal value of two. With further lowering of the temperature, the charge balance around the Ba ion requires an increasingly anharmonic character of the modulation function of Ba, until finally at 10 K a crenel-like shape is assumed for the modulation of this atom.

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Incommensurate cooperative tilting modes of MnF₆octahedra relatedto the structural phasetransitions in BaMnF₄

Cited by 5 publications

References 17 publications

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Structural stability of BaMF₄(M = Mg, Zn and Mn) at high pressures

Ternary fluorides BaMF₄ (M = Zn, Mg and Mn) at low temperatures

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Incommensurate cooperative tilting modes of MnF6octahedra relatedto the structural phasetransitions in BaMnF4

Cited by 5 publications

References 17 publications

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO4

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO4

Structural stability of BaMF4(M = Mg, Zn and Mn) at high pressures

Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperatures

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Incommensurate cooperative tilting modes of MnF₆octahedra relatedto the structural phasetransitions in BaMnF₄

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Structural stability of BaMF₄(M = Mg, Zn and Mn) at high pressures

Ternary fluorides BaMF₄ (M = Zn, Mg and Mn) at low temperatures