Takahiro Ishikawa,Hitose Nagara , Naoshi Suzuki,Taku Tsuchiya, and Jun Tsuchiya
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Transcript of Takahiro Ishikawa,Hitose Nagara , Naoshi Suzuki,Taku Tsuchiya, and Jun Tsuchiya
High-pressure phase of calcium:Prediction of phase Ⅵ
and upper-pressure phases from first principle
Takahiro Ishikawa,Hitose Nagara,Naoshi Suzuki,Taku Tsuchiya,
and Jun Tsuchiya
Shimizu lab. ORII Daisuke
Phys.Rev.B 81,092104(2010)
Contents
• IntroductionWhat’s “High-pressure phase”?⇒An interesting propertyWhat’s “phase ”?ⅥFirst principles calculations
• Motivation• Research• Summary High-pressure phase of calcium:
Prediction of phase Ⅵand upper-pressure phases from first principle
simple cubic
What’s “High-pressure phase”?PressureThe structure change!!
=Structural phase transition(構造相転移 )
Decreasing inter atomic distance by compression
Electronic states change!
bcc
fcc
An interesting propertypressure-induced superconductivity
• Superconductivity(超伝導 )⇒electrical resistance = 0⇒Meissner effect B=0
linear motor car
electrical cable
@ extremely-low-temperature
Normalconductivity (常伝導 )
Superconductivity (超伝導 ) !!
Phase transition!!cool
Matsuoka private communication
①【 Ca- structureⅣ 】Tetragonal P41212 structure with fourfold helical atomic arrangements
②【 Ca- structureⅤ 】Orthorhombic Cmca structure with zigzag atomic arrangement
What’s “phase ”?Ⅵ• Structural phase transitions (構造相転移 ) of calcium
fcc bcc sc (simple cubic) ①
[GPa]20 32 113 139
Ca-I Ca-II Ca-III Ca-IV Ca-V
② ?
⇒ Highest Tc in simple element!
Transition temperature Tc 25K @ 161GPa (Ca- ?)Ⅴ
Ca
First principles calculations
Input data1. Crystal structure2. Type of atoms
Determination of electronic states
Output data1. Charge density2. Total energy3. Stress4. Inter atomic forceetc…
Motivation
BackgroundInvestigating mechanism of high Tc
superconductivity
Predicting the structure of Ca in which the highest Tc is observed
Computational detailsstructure
1. fcc 2. bcc3. sc (simple cubic)4. hcp5. Cmca6. Cmcm7. Pnma8. I41/amd9. P4121210.I4/mcm(0,0,γ)
The most stable structure @ 0K
Input data1. Making crystal structure (lattice
vectors and atomic coordinates)2. Type of atoms⇒structural optimization⇒electronic states
Comparing the enthalpies up to 200Gpa
(enthalpy)
Comparing enthalpies
figure 1
figure 2
(enthalpy)
The lowest ΔH point⇒Most stable structure
Pnma I4/mcm(00γ)
fcc bcc I41/amd P41212
[GPa]3.5 32 109 135
Cmca Pnma
74 117
Ca-I Ca-II Ca-IV Ca-VCa-Ⅲ Ca-VI? Ca-VII?
I4/mcm(00γ)
[GPa]495
Ca-VII?
hcp
Ca-VIII?
I4/mcm(00γ)
fcc bcc sc (simple cubic) P41212
[GPa]20 32 113 139
Ca-I Ca-II Ca-III Ca-IV Ca-V
Experiment
Calculation in this paper
Cmca
Superconductivity• Theoretically ,Tc=25K
was obtained around the phase boundary between Ca- and Ca-Ⅵ
.Ⅶ
50 100 150pressure(GPa)
J.Phys. Soc. Jpn. 75, 083703 (2006).
0 20 40 60 80 100 120 1400
5
10
15
20
25
30
Prediction
pressure(GPa)
Tc(K
) Ca-Ⅳ
Ca-Ⅴ
Ca-Ⅵ
Ca-Ⅶ
Ca-Ⅰ
Ca-Ⅱ
Ca-Ⅲ
Ca-Ⅵ
158(GPa)Experimental result
( Recently , the structure of ⇒ Ca-Ⅵ was experimentally confirmed.)
(Y.Nakamoto et al , Phys.Rev.B , 81, 140106(R) (2010).)
Summary
• The structures of the phases Ca-Ⅵ and Ca- Ⅶ were predicted.
• The highest TC of 25K inthe Ca-Ⅵ or Ca-Ⅶ phase.