aportes de la difracción de - argentina.gob.ar€¦ · los neutrones sirven para... para...

$: Aportes de la difracción de - Argentina.gob.ar€¦ · Los neutrones sirven para... Para discriminar elementos vecinos de la Tabla Periódica. Para localizar elementos livianos en$
Aportes de la difracción de neutrones a diversos problemas en ciencia de materiales

Gabriela AurelioInv. CONICET

Lab. de Resonancias Magnéticas, CAB &Proyecto LAHN

Seminario GIyA - Tandar 26/05/2016

¿Porqué neutrones?Laboratorios de NS en el mundo

Los haces de neutrones son una herramienta cara, pero MUY poderosa. Se aplican a gran cantidad de disciplinas y problemas científicos e industriales.


¿Porqué usar neutrones?

E n qué c as os pueden s er útiles – e inc lus o exc lus ivos – los neutrones ? (en c c ia . de

materia les )Para discriminar elementos vecinos de la Tabla Periódica. CONTRASTE.Para obtener información del bulk y evitar cuestiones superficiales (oxidación, tensiones en la

superficie). Alta penetración, baja absorciónPara localizar elementos livianos en las estructuras (H, O)Para estudiar transiciones de fase (poco problema con entornos de muestra)Para mejorar la resolución de los refinamientos de estructuras (alta intensidad a altos Q)Para estudiar orden magnético

DesventajasLa difracción de neutrones es una técnica muy costosa, y no es una técnica de rutina. Alta

complementariedad con DRX. Concienzuda justificación del experimento. Necesita mucha más cantidad de muestra.


Y porqué?

What causes nuclear scattering? Nuclear forces. Short ranged! Range of the interaction 10-14 – 10-15 m

The range of interaction is much smaller than typical thermal neutron wavelengths

The scattered wave may be described as a spherical wave.

nuclear scattering is isotropicnuclear scattering is isotropic


Interacción neutrón-núcleo

Esquemáticamente, se puede definir el problema como:

z- direction

(incident neutrons)

Vector de scatteringQ

cuando |k|=|k'| (caso elástico)Q y 2q se usan

indistintamente como variables de scattering

blongitud de scattering


The scattering length “b”

The isotropic scattering by a fixed nucleus is described by a single parameter, b, throught Fermi's pseudo-Fermi's pseudo-potentialpotential (Born's approximation)

The interaction potential with a givennucleus N

The position of the nucleus

The neutron'smass

The position of the neutron

The nuclear scattering length


Scattering cross-section: single nucleusB a c k to th e d e te c t o r :

I t tu r n s o u t th a t u s in g th is V (r), th e s c a t t e r in g c r o s s -s e c t io n is

S o th e to t a l n u m b e r o f n e u t r o n s s c a t t e r e d in a l l d i r e c t io n s b y a s in g le n u c le u s is s im p ly

sT O T A L

= 4 p b 2


Some properties of bN

I t is a c o n s ta n t , i t d o e s n o t d e p e n d o n q o r f

I t is a c o m p le x n u m b e r. T h e im a g in a r y p a r t is r e la t e d to r e s o n a n c e p h e n o m e n a b e tw e e n c e r t a in n u c le i a n d th e n e u t r o n (a fe w c a s e s )

W h e n b is p o s i t iv e th e p o te n t ia l V (r) is r e p u ls iv e

I n s o m e c a s e s b is n e g a t iv e : th is a l lo w s fo r c o n t r a s t (e .g . T i-Z r a l lo y s )

T h e r e is n o t a th e o r y o f n u c le a r fo r c e s th a t a l lo w s p r e d ic t in g th e v a lu e o f b

N. I t is ta k e n a s a p h e n o m e n o lo g ic a l

p a r a m e te r a n d d e te rm in e d e x p e r im e n ta l ly fo r e a c h n u c le u s (ta b u la t e d ).


Los neutrones sirven para...

Para discriminar elementos vecinos de la Tabla Periódica. Para localizar elementos livianos en las e s t r u c t u r a s (H , O )

PORQUE LA VARIACIÓN DE b CON EL NÚMERO ATÓMICO ES ERRÁTICA. PORQUE LA VARIACIÓN DE b CON EL NÚMERO ATÓMICO ES ERRÁTICA. PORQUE EL H Y EL O SON BUENOS DISPERSORES DE NEUTRONES Y PORQUE EL H Y EL O SON BUENOS DISPERSORES DE NEUTRONES Y

ADEMÁS PUEDO SUSTITUIR ISÓTOPOS Y MEJORAR CONTRASTES.ADEMÁS PUEDO SUSTITUIR ISÓTOPOS Y MEJORAR CONTRASTES.


Para obtener información del bulk y evitar cuestiones superficiales (oxidación, tensiones en la superficie). Alta penetración, baja absorción

P a r a e s tu d ia r t r a n s ic io n e s d e fa s e PORQUE LA INTERACCIÓN NUCLEAR ES DE PORQUE LA INTERACCIÓN NUCLEAR ES DE MUY CORTO ALCANCE. LA MATERIA ESTÁ MUY CORTO ALCANCE. LA MATERIA ESTÁ PRÁCTICAMENTE PRÁCTICAMENTE VACÍAVACÍA PARA UN PARA UN NEUTRÓN.NEUTRÓN.

Y ta m b ié n p o r e s o , n e c e s i t o m u c h a c a n t id a d d e m u e s t r a



P a r a m e jo r a r la r e s o lu c ió n d e lo s r e f in a m ie n t o s d e e s t r u c t u r a s (a l t a in te n s id a d a a l t o s Q )

PORQUE LA INTERACCIÓN NUCLEAR ES PORQUE LA INTERACCIÓN NUCLEAR ES ISOTRÓPICAISOTRÓPICA Y POR LO Y POR LO TANTO NO DEPENDE DE 2q COMO EN DRX.TANTO NO DEPENDE DE 2q COMO EN DRX.

r ad i ac i ó n C u K α

λ= 1 .91 A



P a r a e s t u d ia r e l m a g n e t is m o d e l m a te r ia l

PORQUE EL NEUTRÓN ES UNA PORQUE EL NEUTRÓN ES UNA PARTÍCULA CON SPIN ½PARTÍCULA CON SPIN ½. POSEE . POSEE UN MOMENTO MAGNÉTICO QUE PUEDE INTERACTUAR CON UN MOMENTO MAGNÉTICO QUE PUEDE INTERACTUAR CON LOS CAMPOS MAGNÉTICOS INTERNOS DEL MATERIAL. LOS CAMPOS MAGNÉTICOS INTERNOS DEL MATERIAL. AÚN AÚN EN AUSENCIA de un campo externo.EN AUSENCIA de un campo externo.

Resulta que la longitud de scattering nuclear (bnuc) y la magnética (bmag) tienen magnitudes comparables. Los picos de difracción magnética son tan intensos como los nucelares.

La interacción magnética neutrón-muestra NO es isotrópica, el scattering decae con Q y por eso sólo se „ven“ picos magnéticos a bajo ángulo.



Pasando del núcleo al cristal

H a s ta a q u í h a b la m o s d e „s c a t t e r in g “ n e u t r ó n -n ú c le o .

To d a s la s „v e n ta ja s “ o p r o p ie d a d e s m e n c io n a d a s v a le n p a r a to d a s la s té c n ic a s : e s p e c t r o m e t r í a s , S A N S , d i f r a c c ió n , r e f le c t o m e t r í a , n e u t r o g r a f í a , e t c .

E l r e s t o d e e s ta c h a r la t r a t a d e i lu s t r a r la m a n e r a d e a p r o v e c h a r e s a s v e n ta ja s a l e m p le a r la té c n ic a d e d i f r a c c ió n d e p o lv o sd i f r a c c ió n d e p o lv o s .


Porqué usar la técnica de difracción de polvos?

Para la ciencia de materiales la cristalografía es una herramienta fundamental→siempre el punto de partida ineludible es el conocimiento de la estructura atómica del material de interés. “Generalmente“ se tiene acceso al material policristalino antes o más fácilmente que al monocristral.

Qué aprendemos de un experimento de difracción de polvo? Hay picos en el difractograma? (cristalinidad)

Qué fases cristalinas puedo identificar? (Id. de fases, bases de datos)

Hay varias fases ? (homogeneidad, impurezas, coexistencia)

Cuánto hay de cada una? (análisis cuantitativo)

Refinamiento de estructuras cristalinas (incluso a veces resolución)

Información de tamaño y tensiones

[Refinamiento (y/o resolución) de ordenamientos magnéticos.]

DRX

Example 1: Metastable phases in Zr-Nb and Ti-V alloys


Metastable phases in Zr-Nb and Ti-V alloys

0 5 10 30 35

400

600

800

1000

1200

1400

Ω (hex)

α (hcp)

β (bcc)

Tem

pera

tura

[K]

Pres ió n [GPa]

Pressure [GP]

Tem

pera

ture

[K] Ti



0 5 10 30 35

400

600

800

1000

1200

1400

Ω (hex)

α (hcp)

β (bcc)

Tem

pera

tura

[K]

Pres ió n [GPa]

Pressure [GP]

Tem

pera

ture

[K]

Zr-Nb

Ti-VTi

„chemical“ pressure

alloying

E

P

D



0 5 10 30 35

400

600

800

1000

1200

1400

Ω (hex)

α (hcp)

β (bcc)

Tem

pera

tura

[K]

Pres ió n [GPa]

Pressure [GP]

Tem

pera

ture

[K]

0 2 4 6 8 10 12 14 16 18 20 22 24

300

400

500

600

700

800

900

1000

1100

1200

Msα q

Ω start

α + ββ

α

% at. NbTe

mpe

ratu

re [K

]

q + q

q + q q

METASTABLE PHASE DIAGRAM

The W phase (high pressure form of Ti, Zr and Hf) can be metastably stabilised by alloying and quenching.

Zr-Nb


Why not XRD?

M a in d r a w b a c k s o f X R D fo r s t u d y in g (c e r t a in ) a l lo y s

X rays probe the s urfac e: that's w here oxides may form, s tra ins from mechanic a l treatments , big g ra ins due to long annea ling times , diffic ulty of powder avera g ing , s ma ll amount of s ample means few g ra ins !

Ordered a lloys us ua lly form w ith neig hbouring elements : very s im ila r s c attering fac tors , s ite oc c upancy hard to s tudy


Advantages of ND

Advantages of using ND in our scientific problem: Metastable phases produced by quenching from HT → avoid surface oxidation

and study the bulk We were interested in possible Zr/Nb or Ti/V atomic ordering in the binary Ω

phase. We needed reliable phase fractions to study phase coexistence in the diagram,

not possible at Centro Atómico with a conventional diffractometer in this kind of samples.

We were interested in evolution towards thermodynamic equilibrium → in-situ thermodiffraction.


Design!

Design of the experiments, selection of instruments Systematics of quenched alloys at RT as a function of alloying content –

constitution of the alloys and lattice parameters dependence with composition → don't need too much resolution with these simple phases, no excessive peak overlap, good accuracy in peaks positions is enough → low or medium resolution diffractometer → D1B (λ ≈ 1.5 Å)

Phase fractions and possible order Zr/Nb or Ti/V as a function of composition

In situ aging – kinetics towards equilibrium phases → thermodiffraction → medium/low resolution BUT many many neutrons (fast!) → D1B, D20

G. Aurelio - WNS2016 -- Bariloche, 10-12 Feb 2016

Neutron powder diffraction

Ins trument D20: hig h flux diffrac tometer a t ILL

Array of He3 detectors at D2B (ILL)

Inte

nsity

[sca

ttere

d ne

utro

ns]

2θ [scattering angle]


The samples

P [

What is a powder for a metallurgist ??

In metals, crystallites are hold together by grain boundaries, but they may develop very big grains, so you will find a „texture“ problem...

Some alloys are very brittle → you can easily crash them and get fine powders, you may sieve them and get to a good specimen for powder diffraction

Other alloys (these ones!) are NOT! To improve statistics, we cut the alloy in tiny pieces, or make shavings before the final thermal treatment (to remove strains). The best solution is to emulate a good powder average by spinning the sample holder. It works nicely thanks to high penetration depth but not possible inside furnaces...


The instruments

D1B medium/high intensity diffractometer, guides hall

Vanadium Sample holders


The data

Data from D1A (ex-high resolution diffractometer at ILL)

l= 1.51 Å

From these data we constructed the systematics of cell parameters and constitution of alloys as a function of composition, at room temperature.


Some results

Experiment @ RT in D1B with l = 1.28 Å on a sample Zr-10 at.% Nb previously aged for different periods @ 773 K and quenched

0 5 10 15 20 25 30 35 40700

750

800

850

900

950

1000

1050

1100

1150

α +βNb

Perovic & Weatherly [97Per] Fernández Guillermet [91Gui]

Esta Tesis : Experimento de termodifracción a 900 K Experimento T/R/T - recocido a 773 K

α +ββ

% at. NbTe

mpe

ratu

re [K

]

From these experiments we studied thermal expansion of the b phase and evolution towards equilibrium.


Some results

In-situ thermodiffraction @ D1B l=1.28 Å for an alloy Zr-18.6 at.% Nb aged at 600 K

After 250 min a second phase nucleates (Ω)

Evolution of cell parameters with aging time in the b and W phases

With these experiments we could study the kinetics of nucleation and growth of equilibrium phases.

Example 2: Study of ternary Cu-In-Sn alloys for Pb-free soldering


New solder candidates are emerging

Remove Pb from traditional Pb-Sn solders Search for new solder alloys

to improve performance and to respond for new demands (higher service temperatures)

-aerospace industry-automotive industry

Search for novel bonding methods to assemble

components

alternative Sn-based alloys:- low Tm - good wettability- low-cost!!

New challenges for the electronic industry


A candidate: Cu-Sn-In

There is a lack of information on solder alloys at intermediate and high temperatures.There is very little information on ternary phase diagrams of Cu and Sn alloys: COST Action 531-Atlas of Phase Diagrams for Lead-free Solders


Intermetallic Phases

Fig.1. SEM image of Cu/Sn/Cu TLP interconnection fabricated at 270°C after 30min.

γ-InSn4 + β-In3Sn ???

δ + ζ ???

η (Cu2In / Cu6Sn5) ???

???

γ-InSn4 + β-In3Sn ???

δ + ζ ???

η (Cu2In / Cu6Sn5) ???

???

Cu-Sn-Cu TLPB after 30min @ 270ºC Cu-Sn48In-Cu TLPB after 7days @ 400ºC

Need to know the phase diagrams!


Why is there a need for neutron diffraction?

B in a r y p h a s e d ia g r a m s C u -S n a n d C u -In a r e c o m p le t e b u t s o m e d is c r e p a n c ie s a r e s t i l l f o u n d in t h e c r y s t a l lo g r a p h y o f IP s .

Te r n a r y p h a s e d ia g r a m s a r e u n d e r m a jo r r e v is io n a n d a s s e s s m e n t . C r y s t a l lo g r a p h ic d a ta a r e s c a r c e a n d fu n d a m e n ta l p o r m o d e l l in g w i t h p h e n o m e n o lo g ic a l a p p r o a c h e s s u c h a s C A L P H A D .

X -r a y p o w d e r d i f f r a c t io n h a s b e e n u s e d w i t h d o u b t f u l r e s u l t s : m a jo r p r o b le m s w i t h p r e f e r r e d o r ie n t a t io n , la c k o f p o ly c r is t a l l in i t y , b ig a b s o r p t io n c o e f f ic ie n t fo r C u K a r a d ia t io n

N e e d o f d is t in g u is h in g e le m e n t s a t e a c h p o s i t io n .

I n -s i t u th e rm o d i f f r a c t io n to s tu d y p h a s e t r a n s i t io n s


XRD attempts

X-ray diffraction Cu-Ka radiationSample manually ground2 independent scans

Binary sample Cu 55 at.%--Sn 45 at.% (Cu6Sn5)

Huge grains!


Neutron diffraction experiments

D2B: high-resolution l = 1.59 Å Horiz. Slits 500 mm (more intensity) 6mm and 8mm V sample holders Room temperature measurements

Alloy preparation:Melting of Cu, Sn and In in adequate proportions. Homogenized for 3 weeks @ 300ºC.Quenched from 300ºC to ice-water.

D1B: higher intensity - thermodiffraction l = 2.52 Å 8mm V sample holders 25ºC < T < 450ºC 1.6 º/min heating ramps – 2 min/numor


Models for the Cu-Sn h phase

Cu2In

C u6S n

5 (5 5 a t% C u )


Phase stability and transformations

As-quenched – 1st heating rampExpt. @ D1B: High-Intensity Powder Diffractometer @ Guide HallSAMPLE: ternary alloy S4: 55 % Cu – 40 % Sn- 5 % In

designrepresentation in the

binary (without In)



As-quenched – 1st heating ramp

3 transitions



2nd DSC peak

1st DSC peak

2nd DSC peak: melting of segregated Sn!



3rd DSC peak η → ε

η → ε transition starts around 445ºC for 5% In

In sample S5 (12%In) the transition is not observed below 500ºC @ D1B nor with

DSC → rapid increase of Tη → ε with In addition!



follow-up of the η → ε transition

during the waiting time at 450ºC (step 3) the transition evolves



quenching from 450ºC (4) - 2nd heating ramp (5)- dwell @ 300ºC (6)



2nd heating ramp

melting of Sn-rich h


Some conclusions

The neutron diffraction and thermodiffraction technique has proven to give precise and valuable information on the phase transitions „suggested“ by in-house methods as DSC.

It would have been quite difficult to obtain this information from XRD, even at a synchrotron

High-resolution experiments were crucial for the correct identification of phases, and details of the crystallographic arrangement (some files in databases should be carefully used!!)

Neutron thermodiffraction may become a valuable tool in the current process of evaluation of Pb-free solders phase diagrams!

References:1. Crystal Structure of Cu-Sn-In Alloys Around the η-Phase Field Studied by Neutron DiffractionG. Aurelio; S.A. Sommadossi; G.J. Cuello - Journal of Electronic Materials Vol. 41, Nov 20122. Neutron diffraction study of stability and phase transitions in Cu-Sn-In alloys as alternative Pb-free

soldersG. Aurelio, S. A. Sommadossi, and G. J. Cuello - J. Appl. Phys. 112, 053520 (2012)


YBaCoYBaCo22OO5+δ5+δ

Derivado de la estructura perovskita ABO3

A

BO

CúbicaaP x aP x aP (“111”)

El óxido YBaCo2O5.5


YBaCoYBaCo22OO5.55.5

ABO3

A (Y3+,RE3+)A´ (Ba2+)

B (Co2,3,4+)

O3-x



YBaCoYBaCo22OO5.55.5

Orden de cationes ABO3

A (RE3+)A´ (Ba2+)

B (Co2,3,4+)

O3-x

A’

A

TetragonalaP x aP x 2aP (“112”)

AA'B2O6



YBaCoYBaCo22OO5+δ5+δ

Orden de cationes ABO3

A (RE3+)A´ (Ba2+)

B (Co2,3,4+)

O3-x

A’

A


AA'B2O6YBaCo2O6

YBaCo2O6-δ

No-estequiometríade oxígeno



YBaCoYBaCo22OO6-δ6-δOrden de vacancias

Vacancias desordenadas en el plano [Y-O] Caso δ=0.5

Vacancias ordenadas en el plano [Y-O] Caso δ=0.5


OrtorrómbicaaP x 2aP x 2aP (“122”)

Co+3 Co+3



Y(Ba,Ca)CoY(Ba,Ca)Co22OO5.55.5 Dopaje con Ca2+

xCa

= 0

Magnetización


Y(BaY(Ba1-1-xxCaCaxx)Co)Co22OO5.55.5 Dopaje con Ca2+

xCa

= 0

xCa

= 0.05

Magnetización


Y(BaY(Ba1-1-xxCaCaxx)Co)Co22OO5.55.5 Dopaje con Ca2+

Magnetización

xCa

= 0

xCa

= 0.05

xCa

= 0.1

Est

abili

zaci

ón d

e un

est

ado

ferr

imag

nétic

o


TermodifracciónInstrumento D20: difractómetro de alto flujo y resolución variable

10% Ca

T[K

]

10% Ca10% Ca

T[K

]


Resultados neutronesx = 0.10

O12

2 P

M

O12

2 fe

rri-S

SO

0 50 100 150 200 250 300

10-2

10-1

100

101

102 xCa = 0

ρ [Ωcm

]T [K]

TMI

0 50 100 150 200 250 300

10-2

10-1

100

101

102

xCa = 0.10

ρ [Ωcm

]T [K]

0 50 100 150 200 250 3007.45

7.50

7.65

7.70

7.75

7.80

7.85

b1

2a1

c1

Lattice Param

eters [Å]

T [K]

Con 10% Calcio

SSO: Spin State OrderPirámides y Octaedros con ≠ Spin


Resultados neutrones

Con 5% Calcio

O12

2 fe

rri-S

SO

O12

2 P

M

O12

2 A

FM-G

+

O12

2 fer

ri-S

SO

xCa= 0.05


Resultados neutrones

Con 0% Calcio

O12

2 P

M

O12

2 fe

rri-S

SO

O12

2 A

FM-S

SO

O12

2 A

FM-S

SO

+O

122

AFM

-G

x = 0


Otro tipo de experimentos empleando crio+horno permitió

E s tu d ia r la e v o lu c ió n d e l o r d e n a m ie n t o d e l o x í g e n o a l c a le n t a r la s m u e s t r a s y la p é r d id a d e o x í g e n o e n v a c í o d in á m ic o

E s tu d io s in -s i t u d e lo s c a m b io s c r is t a lo g r á f ic o s y m a g n é t ic o s a l v a r ia r la n o -e s t e q u io m e t r í a d e o x í g e n o

In t e r p r e t a r c u r v a s d e s u s c e p t ib i l id a d m a g n é t ic a e n

Otros experimentos


The neutron guys

“Novel Magnetic Oxides” group in Bariloche

The synchrotron guys

Gabriel Cuello – ILL, France

Javier Campo – ICMA, Zaragoza, Spain

Michel Kenzelmann -PSI, Switzerland

Fabrizio Bardelli – Italy Rogerio Junqueira-

PradoUFMG, Brazil

Rodolfo SánchezGroup Leader

Javier LohrPhD Student

Ana Laura LarraldePost-doc

Eduardo GranadoUNICAMP, Brazil

Javier CurialeScientist

Gabriela AurelioScientist

Agradecimientos


Lo que se viene

LAH

N

|

LABO

RAT

OR

IO A

RG

EN

TIN

OD

E H

AC

ES

DE

NE

UTR

ON

ES

MUCHAS GRACIAS!

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