University of Groningen Soluble multiferroic hybrids

University of Groningen

Soluble multiferroic hybridsPolyakov, Alexey

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Chapter 2. Experimental methods

This chapter describes the experimental methods used. First, techniques

for hybrid synthesis and templating will be discussed. Then, techniques for

structure determination and related methods will be described. Finally, I

will discuss experimental methods that determine the magnetic and

electron transport measurements in organic-inorganic hybrids.

2.1 Synthesis

Organic-inorganic hybrids by their nature consist of an organic and an

inorganic part1. As was discussed in Chapter 1, hybrids can adopt different

dimensionalities, depending on the inorganic connectivity. This thesis will

focus only on 1D and 2D hybrids. This thesis describes only their growth in

bulk form2 or deposited layer-by-layer to obtain hybrid thin films3.

2.1.1 Crystal growth from solution

Organic-inorganic hybrids are formed by self-assembly from solution by

evaporation of the solvent. Hybrid growth, as discussed in Chapter 1

requires formation of the inorganic backbone, originating from connecting

halogen octahedra, coordinating the metal ions.

As an example, I will describe the synthesis procedure for the organic-

inorganic hybrid CuCl4(C6H5C2H4NH3)24,5. For other hybrid compounds, the

procedure is the same, except for the Ni-hybrids.


24

The general procedure for the hybrid synthesis includes solvation of the

metal halide salt (e.g. CuCl2) and the organic halide salt (e.g. C6H5C2H4NH3Cl)

in stoichiometric ratio in the solvent. First, the organic salt should be

prepared. To obtain the required organic salt, hydrochloric acid is slowly

added to the organic precursor (C6H5C2H4NH2). This reaction is exothermic,

so the flask is cooled in a water bath. The HCl is added until the white

steam is not produced anymore by the solution. The reaction for the

formation of the organic salt for PEA-based hybrid is shown in Fig. 2.1.

Figure 2.1 Preparation of 2-phenylethylammoniumchloride: 2-

phenylethylammonia reacts with hydrochloric acid to form the product.

The resulting product is filtered and dried at 60°C. After that, the organic

salt and the metal halide salts are mixed in stoichiometric ratio in ethanol

and stirred for ~30 minutes. When both precursors are totally solved, the

flask is covered with an aluminum foil with holes to obtain a slow

evaporation. The resulting solution is kept in a furnace at 60°C. The hybrid

crystals of CuCl4(C6H5C2H4NH3)2 are formed by slow evaporation of the

solvent (Fig. 2).

For the Ni-hybrids the synthesis procedure is different. In case of the nickel-

based hybrids a metal precursor (NiCl2*6H2O) is heated in an open flask to

120°C to remove the water. The synthesis procedure is performed in argon

atmosphere in order to prevent exposure of the solution to H2O. Then, the

resulting solution is covered with an alumina foil and kept at 60°C.

Another method to obtain good quality single crystal of Ni-based hybrids is

the deviation of the classic solution growth. In this technique a saturated

solution of the NiCl2 salt and the organic salt is solved in a solution of

hydrochloric acid in ethanol (pH=0.3). Then, the solution is stirred in a

closed argon atmosphere at 80°C. When both precursors are totally solved,

the temperature is decreased by 5°C/hour. In this case, while lowering

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temperature, supersaturation will be reached at some temperature and the

nucleation of the crystals will immediately start, as shown in Figure 2.3.

Figure 2.2 Reaction of 2-phenylethylammoniumchloride with

copper(II)chloride is a self-assembly of the two components. The picture

shows the obtained crystals.

Figure 2.3. Crystals of NiCl3(CH3NH3)2 hybrid (red).


26

2.1.2 Growth conditions and morphology of the crystals

Now I discuss the growth parameters to optimize the quality and the size of

the resulting hybrid crystals. Such growth conditions include aspects such as

that the shape of the container, the growth temperature and the solvent

strongly affect the quality and the shape of the resulting hybrid crystals.

The shape of the container is mainly responsible for the size of the obtained

crystals. This is caused by the fact that structure of the hybrid implies layer

formation, thus crystals tend to grow in the platelet form. Therefore, larger

planar areas of the container will result into larger crystals. Moreover, the

shape of the container also influences the evaporation rate, because the

evaporation rate from an Erlenmeyer container is lower than from a beaker

glass. Thus, best crystals were grown from Erlenmeyer type of container.

The temperature of the hybrid growth is one of the most important

parameters of the synthesis. The temperature determines the evaporation

rate of the solvent, thus, determining the kinetics of the growth process.

This is quite important in order to obtain high quality and large crystals.

Even though hybrids can grow at room temperature, higher temperatures

are preferable due to lower risk of water contamination. Obviously, the

optimal temperature of the synthesis is related to the solvent used. For the

CuCl4(C6H5C2H4NH3)2 hybrid growth from an ethanol solution, a

temperature of 60°C provides the best crystal quality/time ratio.

In order to get the best quality crystals, several solvents have been tried,

namely methanol, ethanol, DMF, acetonitrile, acetone, dimethyl sulfoxide,

water and its combinations. For Ni-hybrids water-free synthesis was

performed. The non-polar solvents offer a poor solubility, and are thus less

preferable to be used. Precursors hardly solve in acetonitrile, while

dimethyl sulfoxide takes 2-3 of months to evaporate and therefore they are

not appropriate for hybrid growth. From an acetone solution separate large

uniform crystals grow on the bottom of the container, however not with an

uniform surface. The solutions of a protic series (propanol -> ethanol ->

methanol -> water) provide progressively larger and thicker crystals, which

means that better solubility result in a larger crystals. The best crystals have

27

been obtained in ethanol and in a mixture of ethanol and about 10% water.

These crystals were large with varying thickness and had a good surface.

Hybrid crystals have the form of platelets, which is caused by weak bonding

in the c-direction. The c-direction of the crystal is held together by weak

interlayer forces. Therefore, this direction has the slowest growth. The

crystals are always oriented with the c-direction pointing up. The a- and b-

directions are more difficult to determine.

The solvent also influences the shape of the obtained crystals as seen in

Figure 2.4. Angles between the facets of the obtained crystal are mostly 90o

when solving in water. Variations caused by the different polarity of the

solvents, influence the in-plane faceting of the crystals.

Figure 2.4. CuCl4(PEA)2 crystals synthesized in a) ethanol b) water and c)

variations in faceting and growth morphologies.


28

The surface profile of the obtained crystals was measured with an AFM

microscope. An AFM picture of a CuCl4(PEA)2 hybrid, grown at 60oC from

ethanol is shown in Figure 2.5 (performed by A. Everhardt during his Top

Master NanoScience studies).

Figure 2.5. a) AFM topology of a CuCl4(PEA)2 surface, b) the phase image, c)

line scan of the topology image showing step sizes of about 2 nm. These

measurements were performed by A. Everhardt.

29

The best crystals show a very flat surface, in which clear steps of 2nm size

can be recognized (Fig.2.5 a, c). Also, the phase image and its line scan

(Fig.2.5 b) display the existence of impurities on these steps which belong to

a different phase than the one of the crystal surface.

Figure 2.6. Crystal structure of the CuCl4(PEA)2 hybrid with important

distances indicated.

The nature of the observed steps can be determined by analyzing the

structure of the hybrid. Figure 6 displays the crystal structure of the

CuCl4(PEA)2 hybrid with the size of the possible steps indicated. From these

distances we can suggest that the most preferably steps are represented by

the PEA-CuCl6-PEA layer of the hybrid between the Van der Waals bonded

molecules (1,93 nm).

2.1.3 Langmuir-Blodgett technique

The Langmuir-Blodgett (LB) technique6 was chosen to synthesize thin films

of the organic-inorganic hybrids. The advantages of this technique are low

temperature processing and the possibility of layer-by-layer deposition. The

LB technique, discovered by Langmuir and Blodgett is one of the earliest


30

techniques which has been commonly used to deposit organic molecules in

thin film form. LB implies the formation of the film from hydrophilic and

hydrophobic parts on the water-air interface under control by surface

pressure. Amphiphilic molecules are spread on the water surface and then

compressed to form a well-ordered monolayer at the air-water interface.

Then, the resulting monolayer film can be transferred homogenously to a

solid substrate by dipping it into the water as sketched in Figure 2.7.

Figure 2.7. a) Amphiphilic molecules spread on water surface, b) molecules are compressed by applying the pressure to form a solid-like phase consisting of one mono-layer and c) the monolayer is transferred to the substrate by vertical dippingthrough water-air interface.

Amphiphilic molecules consist of a polar head and a non-polar tail. The

polar part is hydrophilic, while the alkyl chain (non-polar part) is

hydrophobic. The Langmuir-Blodgett synthesis can be used to generate

complex sequences of different building blocks, yielding a method for

fabrication of heterostructures.

31

Figure 2.8. LB trough used for synthesis of the hybrid film a) front-view and b) side-view. Picture made by O. Floweri. Once a stable monolayer is formed, it can be mechanically transferred to a

solid substrate (hydrophilic or hydrophobic) by moving the substrate

vertically through the water-air interface (Figure 2.7d). Such a substrate also

needs a special treatment. For synthesis of Cu-based organic-inorganic

hybrids, the substrates were sonicated in methanol, then in an 1:1 ratio

solution of methanol + toluene and finally in toluene for 1 minute. Thus, the

surface of the substrate gets hydrolyzed. The substrates were made

hydrophobic through a treatment by an organic solution, namely by self-

assembling a monolayer of dodecyltrichlorosilane (C12H25ClSi) onto the

substrate. In these organic molecules, the SiCl3 functions as a covalent

attachment to the surface, rich in hydroxyl groups, whereas the alkyl part

acts as hydrophobic part. The synthesis was performed by N.Akhtar and is

described in details in the PhD thesis7. A 2% solution of

dodecyltrichlorosilane in toluene (1.5 mL (C12H25ClSi) in 75 mL toluene) was

used. The substrates were placed inside the (C12H25ClSi) solution, sonicated

for 1 min and exposed them overnight in the dark.

To synthesize the Cu-based organic-inorganic hybrid films by the Langmuir-

Blodgett technique, copper chloride is used as the inorganic part, while

methylamine (MA) and octadecylamine (ODA) acts as the organic moiety.

As discussed in Chapter 1, the inorganic octahedra in bulk CuCl4-based

hybrids are formed by six chlorine atoms with the Cu ion in the center. In

the case of films, we expect same organic-inorganic arrangement.


32

Therefore, the methylamine ligands are required in order to reach desired

formation of the CuCl6 octahedra. The subphase used in the experiments,

was an aqueous solution of CuCl2 (1.0×10-3 mol/L) and MA (1.0×10-3 mol/L).

Langmuir films were obtained by spreading a chloroform-methanol (9:1)

solution of ODAH+Cl- (0.15 mg/ml) onto the subphase at 210C. Then, after

solvent evaporation, the molecules were compressed at a rate of 30

cm2min-1 by a movable barrier until a desired surface pressure was reached

and this pressure was kept constant during the whole deposition process.

The compressed Langmuir film was allowed to stabilize for 30 min time

before deposition.

LB films were deposited by vertical dipping of pre-treated substrates into

the subphase at a dipping speed of 5 mm/min. A Langmuir film was

deposited each time the substrate moved across the air-water interface.

Therefore, one dipping cycle (dipping down and taking up the substrate

from the subphase) gives two hybrid monolayers. Further details of the

synthesis are discussed in Chapter 6 of this thesis and in doctoral thesis of

N. Akhtar.

33

2.2 Structural measurements

In this paragraph we will describe experimental methods, used to

determine the crystal structure, morphology, topology and structural phase

transitions of the investigated organic-inorganic hybrids. Also we will

discuss sample preparations for these methods.

2.2.1 Single crystal X-ray diffraction

X-ray diffractometers consist of three basic elements, an X-ray tube, a

sample holder, and an X-ray detector (Figure 2.9). To produce X-rays,

electrons are generated in a cathode ray tube by heating a filament. Thus

by applying a voltage, electrons will accelerated towards the anode, and the

impact of the electrons can produce X-rays. When electrons have sufficient

energy to dislodge inner shell electrons of the anode, characteristic X-ray

spectra are produced.

Figure 2.9. Bruker D8 Venture single crystal X-ray diffractometer8.

The X-ray spectra consist of several frequencies including Kα and Kβ. Kα

consists, in part, of Kα1 and Kα2.9 Kα1 has a slightly shorter wavelength and

twice the intensity as Kα2. The specific wavelengths are characteristic for

anode material. Filtering is required to produce monochromatic X-rays

needed for diffraction. This process is done by foils or crystal

monochromators. Kα1 and Kα2 are sufficiently close in wavelength such that


34

a weighted average of the two can be used. X-ray single diffraction

measurements were performed on a D8 Venture diffractometer from

Bruker using different temperatures with Mo or Cu X-ray anodes. The

crystals for these measurements were carefully chosen using an optical

microscope, using polarization filters when needed. The size of the selected

crystals was limited to 0.2 mm.

Constructive interference occurs when the geometry of the incident X-rays

concurs with the Bragg equation (Figure 2.10):

The resulting X-ray diffraction pattern represents the structure of the

material. The relation between the structure factor and the atomic

scattering factor is:

Figure 2.10: Visualization of Bragg’s Law

λ: wavelength of the X-ray

d: distance between two crystallographic scattering planes

θ: angle between the incoming X-ray and the crystallographic scattering plane

35

where h, k and l are the indices of the diffraction planes (Bragg reflections),

N is the number of atoms in the unit cell and (xj ,yj , zj) are the fractional

coordinates of the j of the atom with scattering factor fj. Each structure

factor represents a diffracted beam with an amplitude |F(hkl)| and a

relative phase. The crystal structure can be obtained from the diffraction

pattern if the electron density function is calculated at every point in a

single unit cell:

The calculation of the electron density results in a corresponding map,

where electron density represents the position of atoms in the cell. The

structure factors are the Fourier components of the electron density of the

crystal structure and vice versa. The well-known “phase problem” is caused

by the fact that the measured intensities of a diffraction pattern allow

determination of the structure factor amplitudes, but not their phases. The

calculation of the electron density is not obtained directly from

experimental measurements and the phases must be obtained by other

methods. When phases and structure factors amplitudes are calculated, a

first electron density map is calculated to obtain atomic positions. To

optimize fitting between the calculated and observed intensities, Fourier

synthesis and structural parameters refinement is performed, which include

positional atomic parameters and anisotropic vibration parameters. Finally,

the hydrogen atom positions are determined or calculated using

conventions. For the organic-inorganic hybrids the hydrogen atoms were

generated by geometrical considerations and constrained to their idealized

positions.

2.2.2 Thin film diffraction

To determine the crystal structure of the films, XRD thin film diffraction

methods were used in a reflective geometry10. X-ray reflectivity can be used

to investigate the density, crystallinity, thickness and d-spacing of films.

Moreover, it is a surface sensitive technique that can be used to determine


36

the thickness of the film. In this technique, the incident x-rays hit the

sample surface at low angles (below 10o). At very low angles (below a

critical angle), the x-rays do not penetrate into the sample surface whereas

above the critical angle the penetration increases quickly with increasing

angle. When they are incident on a multilayered thin film, the x-rays are

reflected from the interfaces where the electron density varies between

two layers.

Figure 2.11. Illustration of the refraction causing Kiessig fringes

The resulting x-ray diffraction pattern consists two kind of peaks: Bragg

peaks (Figure 2.10) and Kiessig fringes (Figure 2.11). Bragg peaks appear

due to the diffraction between individual planes in the film. Using the Bragg

equation, the d-spacing between the planes can be calculated. In case of

layered hybrids, the d-spacing is the repeat distance of the layers.

The Kiessig fringes result from the interference of X-rays scattered at

interfaces. They are a consequence of the angle-dependent phase shift,

with a period that is determined by the total thickness of the film (Figure

2.12). A layered material with n repeat units shows n-2 Kiessig fringes

between two diffraction peaks in the X-ray reflectivity spectrum.

37

Figure 2.12. Example of a thin film diffraction scan of 16 layers of CuCl4(ODA-MA) hybrid. The length of smallest periodic unit perpendicular to the film surface (d) can

be calculated from the position of the diffraction peaks using the Bragg

formula. To determine the peak position more precisely in a rapidly

changing background, the diffraction peaks can be fitted with Gaussian or

Lorentzian line shapes or linear combinations of the two.

Samples, investigated in this thesis were deposited and measured on glass

substrates. Measurements were performed by N.Akhtar7. The film XRD

measurements were done on a Philips X`pert materials research

diffractometer (MRD) equipped with a copper Kα radiation source with

wavelength 1.541 A. The XRD pattern was recorded in a 2theta range from

1 to 10o, in steps of 0:01o with a counting time of 15 s for each step.

2.2.3 Atomic Force Microscopy AFM

Atomic Force Microscopy (AFM)11 is used to determine changes in the

surface topography of a sample by measuring the interacting force between

sample and tip when they are very close to each other (Figure 2.13).


38

Figure 2.13. Schematic illustration of an Atomic Force Microscope12 In AFM, only changes in surface topography can be measured. The detection can

be performed by monitoring the probe or tip displacement when the tip is scanned

over the surface while keeping the force constant. This displacement can be

observed from a laser beam that is directed on the cantilever that supports the tip.

The deflection of the reflected laser beam corresponds to changes in topography

on a rough sample. AFM measurements were carried out with a Digital

Instruments MultiMode AFM equipped with a Nanoscope controller in tapping

mode using silicon cantilevers (Veeco, model RTESPW) by P.Gordiichyk. For each

sample, AFM scans were performed on several surface positions to check the

surface morphology and roughness. The AFM image for the organic-inorganic

hybrid films were taken by 15 scans and in each scan the tip was moved to fresh

sample area.

2.2.4 Scanning Electron Microscopy

Scanning electron microscopy (SEM)13,14 is a method to analyze surface

composition. This method is based on the interaction of high energy

electrons with the surface of the sample. The exposed area of the sample

interacts with focused accelerated electrons and results in various signals

(Figure 2.14).

39

Figure 2.14. Schematic illustration of Scanning Electron Microscope15

Two types of electrons result from this interaction. Firstly, secondary

electrons (SE), produced when an incident electron excites an electron in

the sample, therefore transferring part of its energy. The excited electron

moves towards the surface of the sample and, if it still has sufficient energy,

it exits the surface and is called a secondary electron. Secondary electrons

originate from the top 1-30 nm (depending on the incident beam energy) of

the sample and are used to image the surface composition of the sample.

SE originate from the ionization of electrons of surface atoms, caused by

the impact of the incident electron beam. A local variation in electron

intensity (due to surrounding electric field) creates an image contrast that

reveals the surface morphology. In insulating samples charging effects can

appear caused by exposure to the electron beam. To avoid these parasitic

effects, samples should be deposited on a conduction substrate. In case of

non-conductive samples, the surface can be coated with a conductive

material to avoid charging and increase the number of the secondary

electrons that will be emitted with energies less than 50 eV.

The second type of the electrons is called backscattered electrons (BSE).

These are elastically scattered electrons, which exhibit no energy loss,

backscattered from the surface of the sample. BSE can provide information

on the elements of the surface.


40

SEM images, presented in this thesis were performed on JEOL- JSM-7000F

microscope with the help of Gert ten Brink. Organic-inorganic thin films

were deposited on a gold-coated SiO2 substrate.

2.2.5 Differential scanning calorimetry DSC- thermogravimetric

analysis TGA

Figure 2.15. Schematic illustration of a Differential Scanning Calorimetry

apparatus16

Structural phase transitions of materials when varying temperature were

measured using Differential Scanning Calorimetry – Thermogravimetric

Analysis experiments17. In the measurements the sample and a reference

are heated in a constant heat flow. The difference of the temperature

between both crucibles, caused by changes in the temperature dependence

of the specific heat of the sample with respect to the reference, can be

detected (Figure 2.15).

The experiments were performed using a SDT 2960 (TA) Instrument.

Experiments were performed under argon atmosphere at constant flow of

41

100 cm3/min. Samples were prepared in powder form and measured in

platinum containers.

2.3 Magnetic measurements

In this paragraph we will discuss experimental details of the magnetic

measurements on the organic-inorganic hybrid compounds. Also we will

describe techniques of the magnetic measurements, such as the

temperature and magnetic field dependence of the magnetization.

2.3.1 SQUID magnetometer

Superconducting Quantum Interference Device (SQUID)18 is a very sensitive

magnetometer used to measure extremely small magnetic fields, based on

superconducting coils in a circuit containing Josephson junctions. Using a

superconducting pick-up coil with 4 windings, as shown in Figure 2.16, the

magnetic signal of the sample is obtained. As sketched in figure 2.17, the

magnetic flux from the sample is transferred to a SQUID located away from

the sample in the liquid helium bath through a superconducting connection.

The blue part in Figure 2.17. represents the device’s magnetic flux-to-

voltage converter, while the green part is the magnetometer’s electronics

that amplifies and reads out the voltage from the magnetic flux-to-voltage

converter.

An alternating superconducting current in the pick-up coil is produced while

the sample is moved up and down repeatedly. This current produces a

magnetic flux that leads to an alternating output voltage of the SQUID. By

locking the frequency of the readout to the frequency of the sample

movement (RSO, reciprocating sample oscillation), an extremely high

sensitivity for ultra-small magnetic signals is obtained by the magnetometer

system.


42

Figure 2.16. A superconducting pick-up coil with 4 windings in SQUID

magnetometer.19

Figure 2.17. Flux-to-voltage converter in SQUID.19

2.3.2 Sample preparation

A well-chosen, good quality crystal was placed into a gelatin capsule in a

particular orientation to allow anisotropic measurements. In order to keep

the crystal aligned and in place, dried cotton was added. Holes were made

in top and bottom of capsule to allow the helium gas flow. The capsule was

put into a plastic straw and glues in place, preventing movement of capsule.

43

The end of the straw was covered to prevent the capsule from falling into

the cryostat. The straw is homogeneous and therefore has no contribution

to changes of magnetic flux. The straw was mounted on a dip-stick and

inserted slowly into the SQUID. A magnetic field of the order of 100 Oe was

applied to center the sample in the pick-up coil.

2.3.3 Magnetic measurement techniques

The temperature dependent magnetization measurements were performed

using zero-field cooled (ZFC) and field cooled methods (FC). In the ZFC

method, cooling of the sample was performed in the residual field of the

magnetometer down to 2 K or 5 K. Then, the magnetic field was applied to

increase the magnetization and the measurements were taken while

heating up the sample. FC measurements were performed in the same way,

but the sample was cooled, after applying the magnetic field.

2.4 Electrical transport measurements

2.4.1 Probe stations & cryostats

The measurements were conducting in various conditions, such as high/low

temperatures and electric field. Thus, various cryostats and probe stations

were used.

In order to measure at low temperatures (from 2K to 350K) a Quantum

Design PPMS was used. The PPMS system can cool the sample down to 5K

and impose magnetic fields up to 9 Tesla. For high-temperatures (from

room temperature to 160o C regime, an INSTEC probe station with SuS

MicroTech probes was used.


44

2.4.2 Sample preparations

Before the measurements the organic-inorganic hybrid crystals were dried

in furnace at 60oC. For measurements in the PPMS system, the sample was

glued with varnish on a sapphire plate, which was then mounted to the

PPMS sample holder (Figure 2.18). Platinum wires and silver paste were

used to connect the samples to the contacts on the sample holder.

Figure 2.18. NiCl3-based hybrid, mounted on the PPMS sample holder.

2.4.3 Capacitance measurements

Capacitance is the property of a material to be polarized in an electric field

and related to the dielectric constant by the following equation:

C = ε ε0 A / d Where ε0 is a permittivity of a vacuum, ε is the dielectric constant of the

material, A is the surface of the contacts and d is the thickness of the

sample.

The capacitance of samples is measured by an Agilent 4284A. The sample is

prepared with two conducting contacts, which are placed perpendicular to

the c-axis (out-of-plane). The sample was placed on a glass plate and glued

fixed with varnish. The contacts were made with silver paint. In case of

measurement in the PPMS system, platinum wires were used to make

contacts with the PPMS sample holder. For high-temperature

measurements the INSTEC probe station with SuS MicroTech probes was

used.

45

2.4.4 Pyroelectric current measurements

For polar materials, heating a poled sample through the electric ordering

temperature, the disappearance of polarization generates an electric

current, resulting from charge displacements (Figure 2.19).

First, a material was cooled through the electric ordering transition

temperature while applying a poling voltage. Most of the pyroelectric

current measurements20 were performed with the polarization

perpendicular to c-axis configuration (out-of-plane).

Figure 2.19. Illustration of the pyroelectric current measurement (picture

made by A.Everhardt)

When the sample reached the low temperature phase, the electric field was

switched off and the contacts were shorted to redistribute (compensate)

surface charges. Then, the current was measured during the heating of the

sample through phase transitions, resulting in temperature dependent

current measurement. Pyroelectric current measurements were performed

on an INSTEC probe station with SuS MicroTech probes. Contacts on the


46

sample were made with silver paste. The current was measured with a

Keithley 6517A electrometer.

47

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University of Groningen Soluble multiferroic hybrids