The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation. (Articolo in rivista)

Type

• Articolo in rivista (Classe)
• Prodotto della ricerca (Classe)

Label

• The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation. (Articolo in rivista) (literal)

Anno

• 2003-01-01T00:00:00+01:00 (literal)

Alternative label

• CAMARA F.; OBERTI R.; IEZZI G.; DELLA VENTURA G. (2003)
  The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation.
  in Physics and chemistry of minerals
  (literal)

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• CAMARA F.; OBERTI R.; IEZZI G.; DELLA VENTURA G. (literal)

Pagina inizio

• 570 (literal)

Pagina fine

• 581 (literal)

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• The use of X-ray diffraction analysis and of structure refinement at non-ambient conditions allows understanding the structural changes accompanying a phase transition, as well as to characterise its thermodynamic properties. This is a good example of a high-quality work done on a designed synthetic composition, which allowed understanding of features which cannot straightforwardly be detected in the compositionally more complex amphiboles occurring in nature. (literal)

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• 30 (literal)

Rivista

• Physics and chemistry of minerals (Rivista)

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• Impact Factor 1,671 (literal)

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• Synthesis of P21/m amphibole crystals close to the nominal composition Na(NaMg)Mg5Si8O22(OH)2 and suitable dimensions allowed investigation of the effects of composition on the thermodynamic behaviour of the P21/m<->C2/m phase transition, which had been so far detected and characterised in cummingtonites, (Vacancy)(Mg,Fe, Mn)(Mg,Fe,Mn)5Si8O22(OH)2. The transition was followed during in situ annealing in the T range 25-400 °C by monitoring changes in unit-cell parameters and in the intensities of a set of superlattice reflections. Polynomial fitting of a 246 Landau potential to the evolution of the order parameter with T yielded a Tc of 252+/-3 °C, and Landau coefficients compatible with second order transition. Strain analysis showed that Epsilon1 and Epsilon3 are approximately parallel to the a- and the c*-axes, respectively, and Epsilon2 is constrained by symmetry to be parallel to the b-axis; Epsilon1 is smaller in this sample than in cummingtonites. Single-crystal structure refinements at 25, 140, 270 and 370 °C allowed modelling of the structural changes as a function of T and symmetry. Crystal-chemical analysis suggests that differences in Tc mainly depend on the relations between the aggregate ionic radii of the B- and C-group cations. Short-range ordering according to ANa-M4Na and A(Vacancy)-M4Mg clusters also decreases local heterogeneity and enhance the stability of the P21/m phase. (literal)

Note

• ISI Web of Science (WOS) (literal)

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• F. Cámara a), R. Oberti a), G. Iezzi b), G. Della Ventura c). a) CNR-Istituto di Geoscienze e Georisorse, sezione di Pavia, via Ferrata 1, I-27100 Pavia, b) Dipartimento di Scienze della Terra, Università G. D'Annunzio, I-66013 Chieti Scalo, c) Dipartimento di Scienze Geologiche, Università di Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 Roma (literal)

Titolo

• The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation. (literal)

Abstract

• Synthesis of P21/m amphibole crystals close to the nominal composition Na(NaMg)Mg5Si8O22(OH)2 and suitable dimensions allowed investigation of the effects of composition on the thermodynamic behaviour of the P21/m<->C2/m phase transition, which had been so far detected and characterised in cummingtonites, (Vacancy)(Mg,Fe, Mn)(Mg,Fe,Mn)5Si8O22(OH)2. The transition was followed during in situ annealing in the T range 25-400 °C by monitoring changes in unit-cell parameters and in the intensities of a set of superlattice reflections. Polynomial fitting of a 246 Landau potential to the evolution of the order parameter with T yielded a Tc of 252+/-3 °C, and Landau coefficients compatible with second order transition. Strain analysis showed that Epsilon1 and Epsilon3 are approximately parallel to the a- and the c*-axes, respectively, and Epsilon2 is constrained by symmetry to be parallel to the b-axis; Epsilon1 is smaller in this sample than in cummingtonites. Single-crystal structure refinements at 25, 140, 270 and 370 °C allowed modelling of the structural changes as a function of T and symmetry. Crystal-chemical analysis suggests that differences in Tc mainly depend on the relations between the aggregate ionic radii of the B- and C-group cations. Short-range ordering according to ANa-M4Na and A(Vacancy)-M4Mg clusters also decreases local heterogeneity and enhance the stability of the P21/m phase. (literal)

Prodotto di

• Istituto di geoscienze e georisorse (IGG) (Istituto)
• Metodologie integrate per la conoscenza di processi e materiali geologici e del loro impatto sull'uomo e l'ambiente (TA.P04.014.002) (Modulo)

Autore CNR

• FERNANDO CAMARA ARTIGAS (Persona)
• ROBERTA MARIA OBERTI (Persona)

Insieme di parole chiave

• Keywords of "The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation." (Insieme di parole chiave)

Incoming links:

Autore CNR di

• ROBERTA MARIA OBERTI (Persona)
• FERNANDO CAMARA ARTIGAS (Persona)

Prodotto

• Istituto di geoscienze e georisorse (IGG) (Istituto)
• Metodologie integrate per la conoscenza di processi e materiali geologici e del loro impatto sull'uomo e l'ambiente (TA.P04.014.002) (Modulo)

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• Physics and chemistry of minerals (Rivista)

Insieme di parole chiave di

• Keywords of "The P21/m --> C2/m phase transition in the synthetic amphibole Na NaMg Mg5 Si8 O22 (OH)2: Thermodynamic and crystal-chemical evaluation." (Insieme di parole chiave)