HTXRD In general TA+PXRD course · · 2017-11-15 HTXRD Our tool TA+PXRD course - More HTXRD December 2015, Mikko Heikkilä 17 X-ray windows Gas inlet Gas outlet Vacuum line Turbo

www.helsinki.fi/yliopisto

TA+PXRD coursePart 5, HTXRD, our tool and examples

November 2017, Mikko Heikkilä

TA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 114.11.2017 www.helsinki.fi/yliopisto

High temperature XRD – overview

HTXRD In general• In the early history the main application was high temperature

phase changes

• equipment were developed later for low temperatures and

applications for in situ, time-resolved and in operando studies

• In in situ experiments a system or a material is studied at non-ambient

conditions where chemical or physical processes occur

• In operando requires the system studied to be under identical conditions

as in, for example, an industrial process

TA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 214.11.2017


HTXRD – overview

Why not ex situ, where• Sample mounting is simple (and usually somewhat standardized)

• Samples can be taken from various stages of materials processing

and analyzed in detail

• Complementary studies (optical microscopy, SEM, TEM, elemental

analysis, etc.) can be carried out


HTXRD – overview

In situ enables one to• learn something about how materials are made, how they behave

during heating and how they might change in an application

• make an easier choice for the appropriate temperatures for post

deposition heat treatments and ex situ complementary

• without in situ data, one would need numerous heat treated samples

and/or lot of guesswork to figure out the useful temperatures



HTXRD – overview

Typical experiments:• Dynamic powder diffraction: time-resolved experiments are

performed to follow materials during chemical or physical reactions

and processes

• Static experiments: information about materials under steady-state

conditions in a complex system is obtained, e.g. catalysts in a

reactor at operating conditions, or isothermal oxidation/reduction of

the sample in different atmospheres


HTXRD – overview

Measurement examples• Time-resolved studies:

• materials synthesis (solid state, sol/gel, hydrothermal, thin film growth,…)

• cathode and anode materials in lithium batteries during charge/discharge

cycles

• adsorption/desorption, ion exchange and intercalation reactions of

layered or microporous materials



HTXRD – overview

Measurement examples• catalysts under operating conditions, hydrogen storage materials

during uptake and release of hydrogen or studies of electrochemical

reactions

• materials during physical processes or interactions, e.g.

piezoelectric materials in oscillating electrical fields, studies of

strain/stress development during mechanic treatment of metals or

reaction to changes in an external magnetic field.


HTXRD in short

Non-ambient conditions allows one to see

• Phase transitions

• either reversible or irreversible

• Oxidation/reduction of the sample

• Usually irreversible, unless atmosphere is changed during the

measurement

• Reaction temperatures and products of mixtures

• Irreversible, unless reaction product has a different low temperature

phaseTA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 814.11.2017


HTXRD in short

Non-ambient conditions allows one to see

• Crystallization of amorphous samples

• Thin films deposited at low temperatures are often amorphous and

sometimes require crystallization

• Determination of thermal expansion parameters

• Since XRD is highly sensitive to unit cell size, determining the size as a

function of temperature is usually quite straightforward

• Unlike with dilatometry, XRD allows one to evaluate anisotropic expansion

along different cell axes


HTXRD – overview

Differences to ambient XRD• Atmosphere is something else

• Inert (N2)

• Oxidizing (air, O2)

• Reducing (H2, forming gas (mixture of H2 and N2))

• Moisture controlled

• Reactive if chamber allows for that

• Vacuum



HTXRD

Different chambers• Few manufacturers, e.g. Anton-Paar and Edmund Bühler,

Bruker

• All look quite alike: x-ray transparent windows

in a big block of steel

• Walls kept at room temperature

with water circulation


HTXRD

Different chambers• Heating either by

• direct heating (e.g. Pt strip) allows higher temperatures but less

control on thermal gradients

• heating coil surrounding the sample gives more even temperature

surrounding the sample

• Different atmosphere possibilities depending on the model

• Not very highly reactive gases, though



HTXRD – Anton Paar


HTXRD – Edmund Bühler

High and low temperature ovens• Left: HDK 1.4/2.4 temperature up to 1800/2400 °C

• Right: HDK S1, ambient temperature to 1600°C (standard) or

-185°C to + 400°C (with low temperature option)

• Direct heating in both



HTXRD – Bruker


HTXRD

Our tool• We have an Anton-Paar HTK1200N oven attached to our

PANalytical X’Pert Pro MPD diffractometer

• Both focusing and parallel beam optics work, angular range of the

GIXRD is slightly limited due to the oven design

• Temperatures from ambient to 1200 °C

• Currently available atmospheres include air, O2, N2,

forming gas (10 % H2 in N2) and vacuum (down to 10-4 mbar)

• Reducing atmospheres limited to ~700 °C and require oxidation of the

heating coils afterwardsTA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 1614.11.2017


HTXRD

Our tool

TA+PXRD course - More HTXRDDecember 2015, Mikko Heikkilä 17

X-raywindows

Gas inlet

Gasoutlet

Vacuumline

Turbodragpump

Towardsbackingpump


HTXRD in short

Restrictions when compared to ambient XRD• One can’t stay too long at each temperature if slow solid state

reactions are expected

• Since you never know, as short as possible measurements just in case

• Oven windows absorb 20–30 % of the radiation

• requires equally longer times per step

• Not always possible within short measurement time rule

→ angular range needs to be narrowed



HTXRD in short

About measurement strategies• angular range should be as narrow as reasonably possible, in

order to make faster measurements with acceptable noise level

• Depends on possible phase changes or chemical reactions

• If material is known beforehand, educated guess can be made

by trying to guess the possible products and finding a suitable

range by comparing the reference cards

• Otherwise first a test measurent with wide range and larger T step


HTXRD in short

About measurement strategies• Step size and step time should be determined as instructed in

previous lessons, with the following obvious restrictions

• One should be even more strict on not to measure with too large step

size: definitely not more than seven points over FWHM

• Step time can’t be as long as total measurement time allows due to the

possible isothermal reactions

• IF one wants to determine precise profile of the peak with negligible

noise then it’s either back to RT for measurements, or synchrotron



HTXRD in short

About measurement strategies• when the suitable angular range and other parameters are found,

then one of the following can be programmed

• constant temperature steps from RT to higher temperatures

• if temperature range of interest is known, then quick heating to

~50–100 °C below that temperature and with smaller steps to higher T

• larger steps until range of interest, then with smaller steps

• after the end temperature either cooling down to RT, or similar

ramp towards RT if reversible reactions need to be observedTA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 2114.11.2017 www.helsinki.fi/yliopisto

HTXRD in short

About measurement strategies• Thin films (almost) always in GIXRD, powders in Bragg-Brentano

• With BB it’s possible to keep the detector in static mode, so that it

follows 3° range around certain angle and saves the intensity in

desired time intervals

• Allows one to heat constantly instead of temperature ramps

• However, poorly implemented in current Data Collector software

• BB also allows much faster measurements and therefore smaller

temperature steps (or larger angular range)TA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 2214.11.2017


HTXRD in short

Are the temperatures correct?• Calibration can be done using

• known phase transition temperatures (°C)

• e.g. KNO3 orth. → trig. 128

AgNO3 orth. → trig. 165

Ag2SO4 orth. → hex. 427

Quartz trig. → hex. (a → β) 573.0

• known thermal expansion of some substances (e.g. Si and/or Al2O3)

• better (and more difficult) approach, covers the whole temperature range

• Our device should be within ±10 °C error, probably betterTA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä 2314.11.2017 www.helsinki.fi/yliopisto

HTXRD in short

Are the temperatures correct?• K2SO4 measured with our oven

• Phase transition takes place around 580 °C while the literature

value is 587 °C



HTXRD in short

Is the sample surface position correct?• Problem is that the surface position moves due to the thermal

expansion of the sample holder

• Although parallel beam is more or less unaffected by wrong

surface position, focusing geometry has a large angular

dependent shift due to wrong position


HTXRD in short

Quite often the sample doesn’t remain the same


Sample partlymelted

NH4NO3: new sample NH4NO3 after exposure to humid air

Clinkernew sample

Clinkerafter experiment

ZrO2 after heating to 1300 °C

Examples provided byChristian Resch(Anton Paar)


HTXRD in short

How to deal with the wrong sample surface position?• There are ways to circumvent the sample holder issue

• Move the sample holder with the temperature

• Use internal standard that doesn’t react with the measured substance

• It’s thermal expansion should be known, then the surface position can be

corrected later using Rietveld method

• Possibility to correct the temperature as well

• Sadly no chance for this with coatings and thin films

• Both


HTXRD examples

28Inorg. Chem. Seminar Seriers, Autumn edition 29.9.2010

Often data is presented either in• Three dimensions (left) or two dimensional intensity plot of the

same data(right)

• Pt sample, seems to remain at least partially metallic up to 1175 °C



HTXRD examples

• as peak intensity should in general decrease as a function of 2q,

what happens at high angles? (tip: GIXRD measurement)

• some authors might state that

based on XRD data, the film is

highly (110) oriented

• please, don’t make this mistake

• in this case, (111) planes are

parallel to the surface

• could (and should) be verified with

q-2q measurement and a rocking curve35 40 45 50 55 60 65 70 75

(220)

(200)

Inte

nsity

°2q

(111)


HTXRD examples– crystallization

• ALD grown tantalum oxide is usually amorphous as deposited

• In this case deposited at 325 °C

• heated and measured under nitrogen, crystallizes to orthorhombic

Ta2O5 above 675 °C

from Blanquart, Longo, Niinistö, Heikkilä, Kukli, Ritala, Leskelä, Semicond.Sci.Tehcnol., 27 (2012) 074003(doi: 10.1088/0268-1242/27/7/074003)



HTXRD examples– crystallization + phase change

from Kärkkänen, Shkabko, Heikkilä, Vehkamäki, Niinistö, Aslam, Meuffels, Ritala, Leskelä, Waser, Hoffmaan-Eifert,Phys.Status Solidi A, 212 (2015), 751-766 (doi: 10.1002/ p s sa .201431489)

• As deposited ZrO2 is somewhat oriented but not very crystalline as

deposited

• The cubic and tetragonal phase can be distinguished around 60 °2q

upon heating and cooling


HTXRD examples– oxidation

• ALD grown Rh film

• first weak signs of Rh2O3 phase at 475 °C, Rh fully oxidized >700 °C

from Heikkilä, Hämäläinen, Aaltonen, Ritala and Leskelä, Z.Kristallogr.Suppl.,



HTXRD examples– reduction

• ALD grown IrO2 thin film heated in nitrogen

• Begins to reduce to Ir above 650 °C, fully reduced >750 °C

from Heikkilä, Hämäläinen, Puukilainen, Ritala and Leskelä, ”High temperature XRD study of atomic layer deposited IrO2”,to be submitted



• By doing a Rietveld refinement on the data, the cell parameters of

the IrO2 and Ir phase can be represented as a function of T

• Possibility to evaluate

thermal expansion

from Heikkilä, Hämäläinen, Puukilainen, Ritala and Leskelä, ”High temperature XRD study of atomic layer deposited IrO2”,manuscript ready

0 200 400 600 800 100063

64

65

66

67

68

69

0 200 400 600 800 1000

3.10

3.12

3.14

3.16

3.18

0 200 400 600 800 10004.40

4.42

4.44

4.46

4.48

4.50

4.52

4.54

3.78

3.80

3.82

3.84

3.86

3.88

55

56

57

58

59

60

61

T (°C)

iridiumV (Å3)a (Å)

iridium oxidea (Å) c (Å) V (Å3)




• Heating the same film in vacuum lowers the reduction temperature

over 400 °C

• In this case the reduction is complete at 250 °C

• Crystallinity remains poor up to 500 °C

from Heikkilä, Hämäläinen, Puukilainen, Ritala and Leskelä, ”High temperature XRD study of atomic layer deposited IrO2”,manuscript readyTA+PXRD course - High temperature XRD

November 2017, Mikko Heikkilä 3514.11.2017 www.helsinki.fi/yliopisto


• Heating in actual reducing atmosphere (forming gas (10 % H2 in N2)

lowers the reduction temperature a bit more

• Reduction is now complete at 200 °C, and the Ir phase appears to

crystallize better at lower temperatures

from Heikkilä, Hämäläinen, Puukilainen, Ritala and Leskelä, ”High temperature XRD study of atomic layer deposited IrO2”,manuscript readyTA+PXRD course - High temperature XRD

November 2017, Mikko Heikkilä 3614.11.2017


HTXRD examples– isothermal reduction

• ALD grown Cu2O in forming gas


HTXRD examples– phase change

• What happens in the figure below? At least three phase changes

• 175 °C, 275 °C and 925 °C



HTXRD examples– phase change

• Similar phase transitions in TG


Step -3,0815 % -0,2881 mgResidue 40,3043 % 3,7679 mgLeft Limit 628,30 °CRight Limit 994,16 °CInflect. Pt. 917,57 °CMidpoint 909,26 °C



!rodicrodic, 9,3486 mg

%50

°C50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

%°C^-12

°C50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

Lab: Timo Hatanpää SystemeRTAMETTLER TOLEDO S


Quick and dirty intro to XRR

In XRR• the one dimensional scattering potential (SP) perpendicular to the

sample surface is determined (B-B measurement in very smallangles)

• When the material is layered and it’s chemical composition isknown, the SP can be related to the chemical profile or atomicstructure of the layer(s)• ~electron density

• thickness, mass density and roughness of a single or multiplelayers deposited on some substrate material can be determined



Quick and dirty intro to XRR

Both XRR and XRD are coherent and elastic scattering techniques,but because of the different momentum transfer, the physical reasonfor the interference of reflected waves is different

• in XRR the interference is due to change in the scatteringpotential (or chemical density) wheras in diffraction this is due tothe long range periodical order

• because of this difference, XRR isn’t restricted to crystallinematter


Quick and dirty intro to XRR– the effect of different parameters

general trends for a single layer• critical angle shifts to higher angles when density increases (left)

• the fringe amplitude increases as well

• fringe separation decreases as the thickness increases (middle)

• some effect on the graph shape around critical angle

• larger roughness decreases the fringe amplitude as the angleincreases (right)



How about HTXRR?

Very sensitive to changes in the surface and interfaces might make itpossible to observe the

• surface roughness increase upon crystallization of amorphouslayers

• interface diffusion and possible reaction of amorphous multilayers• interdiffusion of amorphous/crystalline layers before crystallization

of the reaction product


Some HTXRR examples

• indeed it seems that the surface morphology changes at slightly

lower temperatures than the actual oxidation temperature observed

with HTXRD

4429.9.2010

Tox(Ir) > 500 °C

Tox(Rh) > 475 °C Tox(Ru) > 250 °C

44

from Heikkilä, Hämäläinen, Aaltonen, Ritala and Leskelä, Z.Kristallogr.Suppl.,

14.11.2017TA+PXRD course - High temperature XRDNovember 2017, Mikko Heikkilä


Some HTXRR examples

• For Ho2O3/TiO2 multilayer, the diffusion

between the layers is observed at much

lower temperature than the actual

crystallization

from Kukli, Lu, Link, Kemell, Puukilainen, Heikkilä, Hoxha, Tamm, Hultman, Stern, Ritala, Leskelä, Thin Solid Films, 565(2014) 165-171 (doi: 10.1016/j.tsf.2014 .06.039)


End of HTXRD

• During the exercise we’ll

• Setup the oven system including gas delivery

• Make a test measurement ín order

• Determine suitable measurement parameters

• identify the substance and determine the angular range based on that

• Start a measurement and analyze the results later

• More examples during the exercises

• Any questions now are appreciated


Documents

HTXRD In general TA+PXRD course · · 2017-11-15 HTXRD Our tool TA+PXRD course - More HTXRD December 2015, Mikko Heikkilä 17 X-ray windows Gas inlet Gas outlet Vacuum line Turbo