Details

Autor(en) / Beteiligte

• Bogdanov, Evgeniy V.
• Pogoreltsev, Evgeniy I.
• Gorev, Mikhail V.
• Mel'nikova, Svetlana V.
• Мolokeev, Maxim S.
• Laptash, Natalia M.
• Flerov, Igor N.

Titel

Effect of the size of the central atom on the stability of crystalline phases in solid solutions (NH4)3TixSn1-xF7

Ist Teil von

• Journal of solid state chemistry, 2023-12, Vol.328, Article 124373

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2023

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• The effect of a change in internal pressure as a result of partial substitution of the central atom on the realization and stability of the initial and distorted crystalline phases in (NH4)3TixSn1-xF7 solid solutions has been studied. It was found that at a Ti concentration in the range of x = 0.15–0.40, the reconstructive transition Pm-3m ↔ Pa-3 is transformed into a sequence of phase transitions Pm-3m ↔ P4/mbm ↔ P4/mnc ↔ Pa-3. In the (NH4)3Ti0.15Sn0.85F7 solid solution, the first-order phase transition between two cubic phases at T0 = 352 K is characterized by a significant volume jump δ(ΔV/V0) ≈ 1 %, comparable with that in (NH4)3SnF7. An increase of the Ti concentration leads to a strong decrease in the stability of the Pm-3m cubic phase: the first tetragonal P4/mbm phase appears in (NH4)3Ti0.4Sn0.6F7 at T0 = 400 K, which proves the existence of the predicted high-temperature cubic phase in (NH4)3TiF7. In solid solutions, a decrease in birefringence and entropy of phase transitions was observed in comparison with the initial compounds with Sn and Ti as central atoms. The role of critical parameters (unit cell volume, temperature, external pressure) in the formation of cubic and distorted phases is discussed. Stability of phases in solid solutions (NH4)3TixSn1-xF7. [Display omitted] •(NH4)3Sn(1-x)TixF7 solid solutions show rich successions of phase transitions.•Structural distortions of ferroelastic as well as reconstructive origin.•The transformation into the cubic phase Pm-3m predicted for (NH4)3TiF7 was revealed.•Crystal lattice deformation is mainly due to formation of the cubic Pa-3 phase•Three critical parameters characterize the stability of crystalline phases.