IR Spectra ofEnstatite with Lattice Defects
Hiroki. Chihara1, Keisuke. Murata1,C. Koike1, T. Noguchi2 Y. Imai1 &A. Tsuchiyama
1 Dept. of Earth & Space Science, Osaka University
2 Dept. of Science, Ibaraki University

Overview of crystallization experiments
1 Mg1.1Fe0.9SiO4●Formulation of crystallization process ,Si●Crystallization dependency on nucleation process
2 Mg1.1Fe0.4SiO3.5●Fractionation of Mg / Fe between
pyroxene
crystal & amorphous phases

32olivine

1

3 Mg1.1SiO3.1●Activation energy(→Tsuchiyama’s talk),
Mg●Implication to observations(SA)

Fe1 Mg1.1Fe0.9SiO4 (Murata et al. 2007)
Formulation of Crystallization
CIR : Degree of crystallization
κim=(1-CIR)κas+CIRκxt

1 Mg1.1Fe0.9SiO4 (Murata et al. 2007)
Time evolution of crystallization
JMA (Johnson-Mehl-Avrami) eq.

CIR=C∞{1-exp[-(t /τ)n]}n=1.5 : constant number of nuclei
n=2.5 : constant nucleation rate

2 Mg1.1Fe0.4SiO3.5 (Murata et al. 2009a)
fractionation of Mg/Fe between crystal & amorphous phases

3 Mg1.1SiO3.1 (Murata et al. 2009b)
T (K)
1073

1063

1053

1023

106τ (s)105τ = t0 exp (Ea/kBT)
Ea/kB = 1.12 x 105 K(900 kJ/mol)
t0 = 10-40 s

104

103

0.93

0.94

0.95

0.96

1000 / T (K-1)

0.97

0.98

3 Mg1.1SiO3.1 (Murata et al. 2009c)
Chondritic Enstatite with lattice defects

Sample preparation
Amorphous silicate (Mg/Si = 1.07) with Si-alkoxide(TEOS) by Sol-Gel methodhydrolysis: nSi(OR)4+ 4nH2O → nSi(OH)4 + 4nROH

poly-condensation : nSi(OH)4 → nSiO2 + 2nH2OnSi(OR)4 + 2nH2O → nSiO2 + 4nROH

Heating at 790℃ → Crystallized Enstatite

Advantages of Sol-Gel method
Very promising method to produce functional
glass materials in industrial fields !
Homogeneity within the molecular scale
Required temperature is low
Molding is possible
Extremely porous → chemically active

Time evolution of crystallization
1926790oC

14000

2

κ +offsets (cm /g)

12000

clinoenstatite(Chihara et al. 2002)

10000
8000

18 h

6000

6h

4000

4h
3h

2000

1h
Start

020

30

40

wavelength ( μ m)

50

60

70

80

Spectra at room temperature &comparison with single crystals

790℃ 72hours

Spectra at lower temperature
9K50 K
100 K
150 K
200 K
RT
400

102300κ (cm 2/g)κ (cm 2/g)

103

200
100

101

040

42

20

44

46
48
50
wavelength (μm)

30

52

54

40

50

wavelength (μm)

60

70 80 90 100

Summary of spectral features
Far-IR features are different from both ofortho- and clino- enstatite.
some peak strengths are weaker than those of
single crystals (19, 26 micron)at lower temperature prominent featureappear at 48 micron
Broad 69um feature

Ａ crystallized enstatitefrom sol-gel material
stacking faults along to(100) direction

Ｂ clinoenstatite
single crystal

Implication to observations

F.J.Molster et al. 2002

Previous suggestion
on 48 um unidentified feature
Ferrarotti et al. (2000) proposed that
FeSi may be possible carrier of theunidentified the 48 μm feature undera peculiar abundance condition.

Comparison with previous templates
HD44179

MWC922

Traces of similar features in previous studies

Enstatite crystallized
from glass
Fabian et al., 2000

Brucato et al., 1999

Conclusion
IR spectrum of the sample shows different featuresfrom those of single crystals(in particular at 19, 26, 48 & 69 um)
Lattice defects (stacking faults) is thought to be
the cause of the spectral discrepancies
Existence of enstatite with lattice defects issuggested in circumstellar environment.