1

RADIATION DEFECTS AND OXIDATION STATE OF nl- IONS IN NON-STOICHIOMETRICAL OXIDES

Nicolay A. Kulagin

Kharkiv National University for Radio Electronics, av. Shakespeare 6-48, Kharkiv 61045, Ukraine. E-mail: nkulagin@bestnet.kharkov.ua , kulagin@´kture.kharkov.ua

Szczecin May, 7 2007

2

Outline of the talk

- Radiation stimulated by X rays, gamma, electrons and particles charges transfer in oxides: sapphire, garnets, perovskites; - Optical absorption, luminescence, EPR and TSL-TSC spectra of irradiative oxides doped with nd- and nf- ions;- X Ray spectra and oxidation state of component and doped nl- ions; - Ab initio energy calculations for doped and radiation clusters and unit defects;- Electronic state stability of doped nl- ions under radiation of oxides;- Change of oxides surface under plasma treatment: quasi-ordered nano-scale structures;- Shot summary

3

Growth and Treatment

The main methods of crystallization of the oxide single crystals

• Czochralsky - Cz; Verneuil - V;

• Method of horizontal and vertical crystallization - DC;

• Stepanov – S, etc.

Mixtures of different quality and different concentration - C of accidental impurities were used for oxides crystals growth:

* super- pure (C <10-5 wt %),

* pure (C <10-3 wt %), and

* standard one ((C <10-2 wt %)

Thermal treatments and co-doping by Ca, Mg

• O2, 1200 <T <1800 K;

• CO2, 1500 <T <1800 K;

• vacuum, 10-5 Torr, 1500 <T <1900 K;

4

Pure Sapphire – Al2O3

Optical absorption of sapphire grown by different methods

5

TABLE. Spectral parameters of the sapphire grown by different techniques

Sample Abs.edge nm

OpticalBands, nm

AA bands nm

TL, 320-420 nm

TSC peaks T, K

TL bands nm

V 195 206*, 225*,260*, 400* 570

206, 225,280, 475

- 388, 578 690

Vp 142 175, 206,230, 400*

206, 225,280, 475*

4 385, 560507

320, 690690

Vsp 142 185*,206*, 230* No AA 0.1 430, 507*560

420, -690

DC 145 175, 206*235*

206, 230 no TL 398*, 507* -

DCr 142 175, 206,235

206, 230280*, 470*

8 373,506, 565

320, 420690

Czr 143 180*, 206 206, 475 2 430,580

320, 420420, 690

Cr 142 198, 225* No AA no TL 387*, 426*485*

--

Sr 142 175, 206230

206, 230 1 390,418, 430, 506*

420-

Pure Sapphire – Al2O3

6

Ruby – Radiation Effect

Optical absorption of ruby: Al2O3:Cr

7

Structure and Defects

Simplified garnet structure

8

Pure Garnet

• Optical absorption of pure YAG crystals grown by Chochralsky – 1 and HDC – methods

9

Optics of Y3Al5O12:Nd:Cr Garnets – Radiation Effect

Optical absorption of YAG before and after irradiation

10

TSL – TSC spectra for YAG pure and doped with Cr:Nd

11

ESR of Cr+3 ion in Garnet

EPR spectra of Cr*3 ions in YAG crystals

12

Optics of GSGG and GSAG Garnets doped with Cr and Ca

OAS of doped garnets before and after thermal treatment

13

Optics of YAG:V+3 – Thermal Treatment

OAS spectra of V*3 ions in YAG crystals

14

Theoretical Results - Cr+3:[O-2]6 Cluster under Pressure

Table 2. Theoretical values of radial integrals for Cr+3 ions in

Cr+3:[O-2]6 clusters for different R

Integral Free ion / R = 2.1

1.96 1.9 1.8 1.5

Configuration 3d3

F2(3d,3d), cm-1

87080 72010 58644 50932 45863 44795

F4(3d,3d), cm-1 54582 42380 35644 30881 27796 29599

(3d), cm-1 290.9 245.1 220.2 194.8 167.5 74.9

(3d|r|3d ), a.u. 1.093 1.351 1.561 1.721 1.839 2.100

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Theoretical Results - Cr+3:[O-2]6 Cluster, Ruby and YAG

RCr-O(Å)\ Level 2E 2T14T2

2T24T1(t2

2e) 4T1(t2e2)

Theory R = 2.0 Å 14850 15652 16500 22171 24229 37661

1.96 14220 14969 18100 21538 25811 40324

1.9 12500 13113 20500 19392 27659 44176

Ruby

Experiment 14433 15087 18133 21318 24767 39067

Semiempirical 14354 14989 18108 21355 24843 39362

Table1. Dependence of Cr+3 ions energy levels on R Cr-O (cm-1)

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Theoretical Results - Cr+3:[O-2]6

• Table 3. Semiempirical and theoretical data for B, C and Dq for Cr+3 ions in different crystals (cm-1)

DqDqIntegral -Al2O3 Y3Al5O12 Gd3Sc5O12 Gd3Sc2Ga3O12 Cr+3:[O-2]6

B 682 725 740 740 789

C 3120 3373 3578 3578 2829

Dq 1787 1650 1500 1500 1750

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Theoretical Results - 3d2 configuration of Cr+4:[O-2]6

2S+1Γ(t,e) – level Energy, cm-1 2S+1Γ(t,e)- level Energy,cm-1

3T1(t2

2) 0 1T2(t2e) 34909

1E(t22) 15002 3A2(e

2) 38391

1T2(t2

2) 15618 1T1(t2e) 38391

3T2(t2e) 18045 1E(e2) 54429

1A1(t2

2) 30962 1A1(e2) 75683

3T1(t2e) 31939

Table 4. Theoretical level scheme for ion Cr+4 in ruby (Dq = 1990 cm-1, B = 1050 cm-1 and C = 3873 cm-1)

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Optics of Garnets – Cr+4 Energy Levels Schemes

TABLE 10. Energy levels of Cr4+:[O2-]4

cluster

Y3Al5O12 Gd3Sc2Ga3O12

2S+1Γ λtheor, nm λexp, nm λtheor, nm λexp, nm

3A2 - - - -

1E 10950 11000 847 - 3T2 964 964 1052 1052

3T1 640 640 661 600

1A1 627 - 507 504

1T2 517 - 475 504

1T1 453 - 407 410

3T1 410 - 410 410

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Perovskites – ABO3

• LiNbO3:Cr ->

A - Li+, B – Nb+5

• YAlO3:Cr/Nd ->

A – Y+3, B – Al+3

• SrTiO3:V, Mn, Fe, Co, Ni / Pr, Nd, Sm, Tm

A – Sr+2 (RE+2, +3),

B – Ti+4 (Me+2, +3, +4)

• Simplified structure of perovskite

20

Perovskite - YAlO3:Cr:Nd

OAS spectra of Cr*3 ions in YAlO3 crystals

21

Perovskite SrTiO3 Optical Absorption

Optical absorption of SrTiO3 crystals.

Pure (1) and blue sample (2) – a, crystals doped with RE – b (1 - Sm, 2 – Pr, 3 – Nd, 4 – Tm)

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Dielecrical Properties of SrTiO3

0 50 100 150 200 250 300

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0.0045

0.0050

3

2

1

0-1

T[K]

23

Dielecrical Properties of SrTiO3

24

Structure and Defects in SrTiO3

• Energy zones of a wide – band gap crystal with different transitions and local levels

25

X Ray Lines of nlN Ions

X Ray lines: Kα1: 1s1/2 2p3/2 transition

n’l-1nlN- Lα1: 2p3/2 3d5/2 transitionconfigurations

nl- level nlJ- spin-orbit level 3d --------------------- 3d5/2

============= --------------------- 3d3/2

--------------------- 2p3/2

2p =============

--------------------- 2p1/2

1s

============= ============= 1s1/2

26

X Ray Microanalysor

N

ln

N

lnx ll EEE ''''

1 Nx

Nxx EEE

27

CrKα- Line Valency Shift for Irradiated Ruby and Garnet

%, 100 E

E )C(Cr

theorx

expx4

28

Perovskite SrTiO3 X Ray

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Energy of X Ray of RE and AC ions

RE E (K1 ) E(K1) E(L1)

Nd 2+ 37337,290 42250,942 5370,471

Nd 3+ 37336,610 42248,875 5369,708

Nd 4+ 37335,741 42246,471 5368,449

Eu2+ 40071,174 45371,500 5852,357

Eu3+ 40070,420 45369,567 5848,793

Eu4+ 40069,405 45367,192 5847,622

Gd2+ 42921,661 48620,131 6062,622

Gd2+ 42920,521 48618,235 6063,971

Gd2+ 42920,118 48615,998 6060,614

Yb2+ 52156,939 58580,850 7421,563

Yb3+ 52155,897 58578,564 7426,668

Yb4+ 52155,007 58576,031 7429,100

U2+ 95912,345 108809,007 13639,793

U3+ 95912,037 108808,394 13639,528

U4+ 95911,663 108807,659 13639,200

Np2+ 98307,960 111517,588 13970,953

Np3+ 98307,642 111516,963 13970,674

Np4+ 98307,262 111516,221 13970,346

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K1- line L1- line

Ion E0 a -b E0 a -b

Ac 88951.080 0.431 0.070 12671,789 0,424 0.052

Th 91233.519 0.467 0.034 12989,542 0,326 0.032

Pa 93553.072 0.540 0.034 13311,565 0,479 0.030

U 95910.145 0.605 0.033 13637,868 0,539 0.029

Np 98305.122 0.659 0.032 13968,481 0,580 0.028

Pu 100738,542 0,691 0,031 14303,356 0,640 0.027

Am 103210,648 0,724 0,030 14641,226 0,682 0.026

Cm 105721,613 0,767 0,028 14986,249 0,711 0.025

Bk 108272,134 0,826 0,026 15334,323 0,728 0.023

Cf 110862,572 0,882 0,025 15686,806 0,740 0.021

Es 113493,397 0,920 0,024 16043,560 0,784 0.021

Fm 116165,234 0,935 0,023 16405,048 0,790 0.020

Md 118877,847 0,977 0,022 16770,396 0,851 0.020

No 124428,762 1,035 0,021 17140,694 0,875 0.019

320 NcNbNaEEx

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SEM Picture after SrTiO3:Sm Plasma Treatment

32

SEM Picture after SrTiO3:Tm Plasma Treatment

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SEM Picture after SrTiO3:Nd Plasma Treatment

34

3D- AFM Picture after SrTiO3:Sm Plasma Treatment

35

3D-AFM Picture after SrTiO3: Ni Plasma Treatment

3

Energy Levels Scheme Parametrization of nl(f)- Ions

5

Theoretical Foundations

Free IonsHFP approach

Doped CrystalsHL-SCF for Clusters

),()(),(),()( int RrRERrRrHrH lllfree

)|(),|(),(

),(),(),(

11

22

22211112

221111

GlnYRrlnAPGln

GlnGlnGlnln

iii Niii

Niii

Niii

NNNN A

38

Theoretical Foundations – Ions and Hamiltonians

ji

jiji

iji i

iifree )s1(r/1r/Z2/1H

jimn

mjnijimn

nimjni ji

jini srrZH,,,,

int )1(/1/2/1

Ion – nlN: Me – 3dN, RE - 4fN, AC - 5fN => ME The main configurations: nlN and nlNn’l’N’ Cluster: ME+n: [L]k. Ligand – O-2, F-, Cl- etc

6

Theoretical Foundations – Energy of Cluster

)EEE(kkEE)]L[:ME(E excZ'

1freekn

,

,

,)(YB)nl()J,SLSL(

)nl,nl(F)LS,l(fE)LSJ|(nlE

i,q,kiikqkq

''

kk

'Nk0

'Nfree

40

Theoretical Foundations – Radial Integrals

''1

''21

2

''21

2

,)'|''()|''()|''()|()'',(

,)|''()|()'',(

,)|()|(),(

drdrrlnPrlnPr

rrlnPrnlPlnnlG

drdrrlnPr

rrnlPlnnlF

drdrrnlPr

rrnlPDnlnlF

k

kk

k

kk

k

k

kk

41

Theoretical Results - 3d24p configuration of Cr+3 in Cr+3:[O-2]6

Integral Free / R(Å) = 2.1 1.96 1.9 1.8 1.5

Configuration 3d24p

F0(3d,4p), cm-1 91284 65490 69606 71629 74294

F2(3d,4p), cm-1 22295 9455 12485 14705 21010

G1(3d,4p), cm-1 7778 2513 4924 7046 14430

G3(3d,4p),cm-1 7193 2001 3838 5471 11135

(3d), cm-1 331.9 322.1 303.8 288.7 238.1

(4p), cm-1 642.0 97.6 129.6 153.3 198.8

(3d|r|3d) a.u. 1.018 1.064 1.148 1.219 1.474

(4p|r|4p) a.u. 2.734 3.538 3.314 3.210 3.045

(4p|r|4p) a.u. 2.734 3.538 3.314 3.210 3.045

ΔE(3d3–3d24p), eV 17.8 21.8 16.1 9.9 11.6

42

Self Consistent Field Equations for nl-Ions in Solids

nnlnnl rlnPrnlXrnlP

r

llrnlY

rdr

d

'

' ),|()|()|()1(

)|(2 ''

2'

2

2

'l'n,1k,k

'1kk

1kk'll

''''1kk

1kk'll

)]r|'ln,nl(Yb)r|ln,ln(Ya[2/r)r|nl(Y

''

1

1

1

1'

,,

'''' )|(])|,([)|(lnkk

kkllkk

kk

llrlnPrrlnnlYrnlX l

43

''''''121

'' 21

1)|()|(),()|,( drrrlnPrnlP

Rr

kkkrlnnlYk

k

k

kk

)||)(|(

*)|()()||(

'2

'11221

'12

'21

'''2

;1

11221

'22'

22

'11

'22

'22

'11

1'

mmrmmmm

mmOOvSSAmmrmmOOvam m

mm

mm

mm

mmmmmm

kk

ll

m

mm

mm

mm

kk

llmmrmmmmOOSSAvb )||)(|()( ''

11

12'21

'21

'' '

22

11'11

1'

Self-Consistent Potential for nl-Ions in Solids

44

m

mmmm

kk

llmmrmmOOSSAv ,)||()( '

1'2

11221

'''22

'11

1'

mZ

mm

mmmmmmkkll

mrmmmOOmmOR

vZ )'||)(|()[|(

'2

11212

'11

22

'11'11

;11'22

'

Self Consistent Field Equations for nl-Ions in Solids

Boundary conditions: P(nl|r)| r →∞ → 0 - for unit center or impurity ionWigner-Zeits conditions: ∂P(nl|r)/∂r | r→R → 0 for cluster and crystal

7

SCF Potential and Radial Wave Functions for nf- Ions

46

Short Summary

Ab initio study of the electronic structure of ME+n:[L]k-clusters and energy of X-ray lines is a powerful and effective method of investigation of foundations of doped materials. This method and optical spectra of nl- ions in oxides - on the one hand and study of the influence of irradiation or thermal treatment to crystals doped with d- or/and f ions on the other hand allow to explain of the nature of radiation defects into doped oxides and draw the simple conclusion that stability of the oxidation state of ions in crystals is determined relation of energy of ionization of ME+n ion – I Me

and Madelung's constant αM = - ΣZi/ri for the cation site.

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Concluding Remarks

• Crystals growth method determines the main defects of the oxides through crystals stoichiometry

• Crystals stoichiometry determines electronic state and ions valency and properties of the oxide single crystals, too

• Relation A/O changes:- for simple oxides up 0.95 to 0.99- for garnet crystals A/B changes up 0.9 to 0.98- for perovskites - 0.8 – 0.98 (A1-xB1-yO3-z)

• Value of A/O and A/B is determined by possibility of the regular nd and nf ions to change their valency. We can used non-stoichiometry oxides for expansion of area of employment of the pure and doped single crystals