CONCLUSION OF SENSOR STUDIES IN FERROELECTRIC

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1 CONCLUSION OF SENSOR STUDIES IN FERROELECTRIC 7.1 HIGHLIGHT OF FERROELECTRIC SENSOR SUCCESS The nonlinear behaviour of ferroelectrics suggests that they should be useable as frequency multipliers, mixers, amplifiers and logical devices. Such applications have been demonstrated but have nat led to practical use because all these functions can be more economically met by transistors, particularly when they form part of integrated circuits, Ferroelectrics have the disadvantage of instability with temperature and gradual but significant change in properties with time. It remains worthwhile describing some of the efforts to utilize ferroelectric in this way, partly to illustrate there limitations and in future development particularly in electro-optics, integration of electronic and optical functions and capacitors gas sensor, which may revive interest in this type of device. 7.2 CONCLUSION Chapter Ill Triglycine Sulphate and triglycine selenate are relatively old ferroelectric material. These materials show their ferroelectric behaviour near the room temperature (Tc for triglycine sulphate is 49'C and Tc for triglycine selenate is 22 C) triglycine selenate and IX2

2 tr,glyc1ne selenate crystals were prepared by the slow evaporation method form the aqueous solution havening appropriate value of glyc1ne and H 2 S0 4 / H 2 Se0, These crystals were characterized by vibrational spectroscopy and XRD. The so,' and Se0, 2 are H-bonded in triglycine sulphate and triglycine selenate crystals with glycine -1, where as G II /G Ill are strongly H-bonded and forms the dimmer. Due to the different ionic character of so,> /Seo.' the sensing response, i.e; the binding of vapours to anions are different in these cases. The four internal vibrations in SO/' I Se0, 2 ' appeared at v, = 980, Vz = 450 /456, v, = 1180, 1220 and v 4 = 632/625 em '. In IR spectra v 1 was very weak, where as v 3 was strong as expected. The more strong v 3 of So.' with respect to Seo.' reflect this fact. A brief review of the literature relevant for triglycine sulphate I triglycine selenate for the gas.1 vapour sensor applications are presented. The literature survey revels that glycine base materials were not earlier tried for!l'uch sensor applications. Owing to the fact that, these materials show the ferroelectric properties at room temperature, they could be the potential candidates for gas I vapour sensor application. These sensor studies of triglycine sulphate and triglycine selenate were dealt with the sensing of (vapours of organic compounds) voc s such as Methyl alcohol vapours Ethyl alcohol vapours Aniline vapours Ammonia vapours For the alcohol vapour sensor studies triglycine sulphate pellet of area 0 73 em' and th1ckness 2 4 mm was taken This experiment

3 was performed at a room temperature at humidity of 55-60% These stud1es were under taken for the vaflous vapour concentrations of methyl alcohol., e. 5ppm. 10ppm, 15ppm and 20ppm 1n air with 1ts ambient. The response time varied from 3.5 sec to 5.?sec and the recovery time varied from 180 sec to 235sec. Thus conforming the cyclic behaviour. These changes were linear and latter attained the saturation, indicating the sensitivity and stability of the sensor material towards methyl alcohol sensing. The changes in electrical parameter i.e., A.C. conductance and capacitance were recorded. The change in A.C. conductance and change in capacitance with respect to the alcohol concentration showed a linear change. The studies of the pyro electric behavior of triglycine sulphate in the presence of methyl alcohol vapours were also under taken. The ethyl alcohol sensor studies were made for the triglycine sulphate pellet of same dimension at the room temperature at relative humidity of 55-60%. The various alcohol concentrations of 5.7ppm, 10.2ppm, 15.3ppm and 25ppm was mixed in air with its ambient. The response tim-es were small which varied from 2.1 sec to 7. Osee where as the recovery time of triglycine sulphate pellet changed from 75 sec to 120sec. Thus conforming the cyclic behavior of the sensor activities. These studies of response time and recovery time in terms of alcohol vapour concentration in air was quite significant to show the sensitivity of triglycine sulphate towards ethyl alcohol vapours. The changes in electrical parameter i.e., a.c. conductance and capacitance were recorded. The change in a.c. conductance and change in capacitance with respect to the alcohol concentration showed a linear change. The studies of the pyro electric behavior of triglycine sulphate in the presence of ethyl alcohol vapours were also under taken. On the same line triglycine selenate pellet of area 1.13cm 2 and thickness 1 8 mm was also tried for sensing alcohols, aniline and ammonia. The experrment was performed at room temperature at relatrve humidity 50-54%. The change in a.c. conductivity and I X-1

4 change 1n capacitance in terms of var1ous concentrations of alcohols. an1l1ne and ammonia vapours in a1r at ppm level showed the sign1f1cant sensor activity of tnglycine selenate. The vanous concentration of ethyl alcohol used for triglycme selenate sensor studies were 10.8ppm, 15.3ppm, 20.4ppm, 43.4ppm, 64ppm. and 65.?ppm similarly for the sensing of methyl alcohol vapours; the concentrations used were 2ppm, 5ppm, 1 OpP,m. 28ppm and 40ppm. These sensor studies were performed simultaneously for analyzing the sensitivity, stability of triglycine sulphate and triglycine selenate sensor materials towards these alcohol vapours. Further the triglycine sulphate and triglycine selenate sensor studies were undertaken for observing the changes in the electrical parameters. This change was recorded by mixing aniline vapours or ammonia vapours in air at different concentrations. Here aniline is an organic compound and ammonia an inorganic compound. The behaviour in the electrical activities of triglycine sulphate and triglycine selenate pellets in the presence of these compounds was under taken. Triglycine sulphate pellet of same dimension was used for aniline and ammonia sensor studies at room temperature of and humidity of 55-60%. The various concentration of ammonia used for the sensor studies were 2.7ppm, 8.1ppm, 19ppm, 27ppm and 40.8ppm. The response time and the recovery time were recorded. The next part of the studies is related to the aniline sensing by triglycine sulphate pellet. The various concentrations of aniline vapours tried for sensing were 5.?ppm, 13.3ppm, 22.8ppm, 34.3ppm, and 38ppm at the room temperature humidity between 55-60%. The recovery time and the response time in these case was more than the response time and recovery t1me taken for triglycine sulphate pellet for sensing the alcohols

5 The plots for response time and recovery t1me vis concentration of ammonia vapours were linear and the nature of these plots Indicated the good sensitivity of triglycine sulphate towards the ammonia sensing. The a.c. conductivity and capacitance were also recorded during the change in concentration of ammonia vapours and change in conductance and change in capacitance vis concentration of ammonia vapours were curve-liner and the slopes were sufficiently large enough to describe the sensitivity of these sensors towards ammonia vapours. The response time and recovery time was good. The plots between response time and recovery time vis concentration of aniline vapours showed better sensitivity through their slopes and also represented the cyclic behaviour. The response time and recovery time slopes were appreciably good in terms of the sensitivity verification conductivity studies and of triglycine sulphate pellet. The A.C. capacitance studies resulted in to the plots for change in A.C. conductivity vis concentration of aniline vapour and change in capacitance v/s concentration of aniline vapours. The slope of the curve indicated that the triglycine sulphate is potential candidate for the sensing of aniline vapours. The selectivity was. also possible through this sensor for ammonia and aniline vapours. The A.C. conductivity increased from 8.8mS to 9.7mS for 2.7ppm of ammonia vapours, where as this increase was 10.1mS for 5.7ppm of aniline vapour as sensed by triglycine selenate pellet. The same tnglycine selenate pellet of area 1.13cm 2 and thickness 1.8 mm was used for sensing the aniline vapours of concentrations 3.5ppm, 17.4ppm, 22.2ppm, 34.4ppm, 52.2ppm at room temperature and humidity of 50-54%. The response time was very small as compared to the very large recovery time. The change in A.C. conductivity and change in capacitance with the change in aniline vapour concentrations was appreciably good and the plots between response time vis concentration and recovery time vis aniline concentration had the slopes sufficiently large to explain the IXil

6 sens1\1v1\y of tr~glyc1ne sulphate pellets towards the an1line sensing The A C conduct1v1ty stud1es and capacitance studies of triglyc1ne selenate sensor towards the aniline sens1ng showed the regular change 1n conductivity with the change in capacitance with the concentration. The plots for these studies were effective to explain the sensitivity of triglycine selenate towards aniline vapours. As the room temperature increased from 22 C to 27 C, triglycine selenate showed 1ts para electric behavior, due to this the A.C. conductivity decreased with the increase in temperature of the triglycine selenate pellet placed in air with aniline vapours. Ammonia vapours sensing was also tried by using the triglycine selenate pellet. For the various concentration of ammonia vapours such as 8.16, 12, 19, 30 and 54 ppm the slopes of the plots between response time and recovery time v/s concentration of the ammonia vapours were good enough to justify the sensitivity and the cyclic behaviour. of triglycine selenate pellet towards the ammonia vapour concentration in air. Subsequently the change in a.c. conductivity and change in capacitance were also recorded. The plots between the change in a.c. conductivity and change in capacitance with respect to the various concentrations of ammonia vapours were linear and quite significant to show the sensor activity. CHAPTER IV SECTION The characterization of NaN0 2 pellet was done by vibrational spectroscopy. This crystalline structure was further confirmed by the XRD studies. The NaN0 2 pellet of area 1.36cm 2 and thickness 2.01 mm was used for these studies. These studies were performed at room temperature of 32oc for different humidity's of 23%, 26%, 30%, 35%, 40%, 45%, 50%, 55% and 60%. The plots between % humidity vis 187

7 .' a c. conductivity and % humidity vis capacitance show the l1near change, thus conforming the humidity sensor behaviour of NaNO,. The plots between % humidity vis t.o and % humidity vis t>c were obtained in the form of a straight line. The initial value of ac conductance (o) and capacitance (C) was obtained, by the removal of the humidity. This confirmed the cyclic behaviour of NaNO, while sensing the humidity. In the second part the electrical behaviour of NaN0 2 was studied in the influence of ethyl alcohol vapours in air. These studies were made for the various concentrations of alcohol i.e.; 3.06ppm, 5.1 ppm, 7.14 ppm, 10.2 ppm and 15.3 ppm.the response time changed from 3sec to 6.5 sec and the recovery time changed from 10 sec to 37 sec. The behaviour of NaN0 2 in ethyl alcohol vapours in terms of response time and recovery time and the behaviour of t.o and t.c v/s alcohol concentration were good enough to under go these studies. SECTION II Pervoskites ceramics of stanates (A80 3 ), where A= Sr. Ca,Ba andb= Sn. These newly found relaxor materials are investigated for humidity sensor application. The solid state reaction is used to prepare these compounds, the structural characterization and the verification of single phase was done through XRD and surface studies by scanning electron microscope and by vibrational spectroscopy. The observed XRD pattern shows the preparation of single phase and good quality compound supported by the IR spectra. The SEM analysis shows the homogeneous grain size of the sample. The brief review of the literature relevant for the humidity sensor application and related compounds is presented. which show that stanate based ceramics materials are not earl1er tried for gas sens1ng application. owing to the fact these mater1al show relaxer ISS

8 propertres above room temperature They could be the potentral candrdates for humrdrty sensor applrcation The investigatrons of these three samples show The temperature dependent change in conductivity as a function of humidity comes out to be maximum for CaSnO, and minimum for BaSn0 3 This is co-related with the different ionic characters associated with the ionic interactions with BA /Ca /Sr with tin as revealed by the IR spectra, where as the broad band at 630 em ' associated with the cation and an ions is, max for Ca and min for Ba. Electrical conductivity is mainly due to the water molecules filled in the pore and developing the parallel resistance. The comparative studies of ferroelectric material NaN0 2 and relaxor materials AB0 3 show that they were sensitive towards the humidity sensing in terms of ac conductivity and change in capacitance, it was further seen that ferroelectric materials was more sensitive than the relaxor material concluding that ferroelectric NaNOz is a better candidate for the humidity sensing. Chapter V Phthalocyanine shows the non-linear electric behavior. The characterization of Nipc, Cupc and Hpc were done by vibrational spectroscopy. The sensor studies of these ferroelectric related materials were done for sensing fuel vapours. sensing of adultered petrol The sensor studies of NiPc and HPC were done. by palletrzing them. Where as CuPc was taken in the form of vacuum deposrted thin frlm

9 The Nipc and Hpc sensor studies were performed for sensing vapours of unleaded petrol, Kerosene oil and LPG, where as Cu phthalocyanine sensor in the form of thin film was used for sensing leaded petrol vapours. The sensor studies were made, by observing the change in A.C. conductance and the change in capacitance. Hpc pellet of thickness 1.48 mm and area of 1.15 cm 2 was taken with the equivalent air capacitance of 35 nf. The cr 1 n 1 (initial conductance) as 4.8 ms and C;n; (initial capacitance) as 0.001v.f at the room temperature of 42 C to 46 C and humidity of 60% - 65%. The volume of kerosene oil vapours used for the sensor studies were 17ppm, 34ppm, 65ppm and recovery time for these concentrations were made and the change in A.C. conductivity and change in capacitance as the function of concentration of kerosene oil vapours were also under taken for the studies for the sensitivity of the Hpc sensor. Where as recovery time shows the stability and cyclic sensor behaviour of Hpc sensor towards the kerosene oil vapour and LPG vapour sensing. The Hpc sensor showed the positive results for sensing these vapours. Further studies included the sensor behavior of Hpc towards the unleaded petrol vapours adultered with kerosene oil vapours content. The kerosene oil content was kept unchanged i,e; 42.4ppm, and the un leaded petrol vapours were changed to 3.4ppm, 8.5ppm, 23ppm; It was seen that the response time and recovery time increased. This cyclic behaviour shows the reuse as well as the sensitivity of this sensor material. The results thus obtained were quite promising and showed the potentiality as a fuel sensor. In the series of metal phthalocyanines sensor studies, next material undertaken for these studies was nickel phthalocyanine. The studies of Ni phthalo-cyanine were also encouraging for sensing unleaded petrol (ULP), kerosene oil and ethyl alcohol vapours and LPG. In these studies ac conductance and change in capacitance, 190

10 response and recovery time were recorded to study the cyclic behaviour of the Nipc. The pellet of Nipc of thickness 1.52mm and area 1.21 cm 2 with the equivalent air capacitor of the value 2.15nf and initial capacitance of 0.007J.1f and initial conductance of 1.32 ms at the room temperature of and humidity. Various concentration of ULP vapours i,e,; 43.4ppm, 72.4ppm, 108ppm and 207ppm were introduced.inside the chamber. The sensing of ULP in air are shown in various plots. The plot between response time and recovery time as the function of concentration of ULP is shown in fig 5.5, the response time of Nipc increases from 13 sec to 44 sec and the recovery time from 35 sec to 144sec. The various concentration of kerosene oil vapours of concentrations 65, 130, 170 and 195 ppm, ethyl alcohol vapou,r concentrations of 102, 217, 260 and ppm and LPG of concentration 100, 120 and 150 ml were also tried. The results confirmed the sensitivity of Nipc. The sensor studies of copper phthalocyanine were made in the thin film form. These studies of cu phthalocyanine were also encouraging for sensing leaded petrol, kerosene oil and ethyl alcohol vapours and LPG. In these studies change in ac conductance, change in capacitance, were recorded to study the sensitivity of cupc towards the fuel vapours. Chapter VI This chapter presents the characterization of ferroelectric materials for (thermo dielectric energy conversion) TDEEC energy transducer sensor. These studies were conducted for hard ferroelectric mater1al i e for few titanates and few niobates. I'll

11 1. TITANATES 1. Strontium titanate. 2. Barium titanate. 3. Bismuth titanium titanate. 4. Lead zirconate titanate. 2. NIOBATES 1. Lithium niobate. 2. Cadmium pyro niobate. 3. Lead meta niobate. 4. Bismuth titanium niobate. The studies were related to trapping the solar energy or thermal waste energy from the industries. The factors on which the energy conversion depends are specific heat, density, co-eff of thermal expansion, dielectric strength and break down potential of the material. The main emphasis of these studies was given to study the energy converston, for the materials having high dielectric constant and high dielectric strength. Therefore these studies were concentrated on the variation of dielectric strength Eo, di electric constant 6 and co-eff of thermal expansion p of the ferroelectric materials. The TDEEC ratio r was thus estimated. The results thus obtained were quite promising. The effective factors considered as the cause of TDEEC were Co-eff. of thermal expansion, dielectric constant and breakdown potential. The co-eff of thermal expansion was changed for an interval of 0.25 X 10 1 / C. Similarly E 0 and 6 were also changed for small intervals. The energy ratio r for titanates was, between and 0.83 and the energy ratio r for niobates was found to vary between and

12 The small change in the values of- dielectric strength e or the coeff of thermal expansion p or the break down potential Eo, there was a significant change in r. This change of energy ratio was above and up to the maximum of CONCLUSION: Sensors from semiconducting metal oxides have the desired feature of low cost, good sensitivity and convenient form of response. These sensors show a reasonable reproducibility, stability and selectivity by taking all possible precautions into consideration. The reversible redox properties and cyclic stability of phthalocyanine compounds make them useful as active component in sensor devices. Phthalocyanine's have become potential candidate for producing useful and viable material for sensor applications. The d,esign and fabrication of electronic sensors from ferroelectric \ferroelectric related materials are interdisciplinary in nature, and it is possible to manufacture useful devices only through close coordination between physicists, chemists and microelectronics engineers. 7.4 PROPOSAL FOR FUTURE: The principle of the capacitor is formulated simply by the expression for capacitance as a function of the dimensions of the capacitor and the di-electric constant of the medium. The gap distance of the capacitor is the parameter that varies with the measurand. The advantages of capacitive sensors include relatively simple construction and low inherent temperature coefficient. The care must be taken to avoid stray capacitance due to the leads. 193

13 The atomistic understanding of controlled electron and ion transport parallel and perpendicular to the surface normal of extended sandwich structures is the key to many applications of chemical sensors now and in future. Sensor arrays are of increasing importance. Triglycine sulphate/triglycine selenate or phthalocyanine's can be used here as they show high selectivities and sensitivities towards the detection of different molecules. The data analysis from the electronic-nose approach of the sensor arrays and subsequent pattern recognition will make it possible to characterize gas mixtures quantitatively or odors qualitatively. The detailed studies of sensor mechanisms may help to understand the miniaturization of transducers.

CHAPTER 6 DIELECTRIC AND CONDUCTIVITY STUDIES OF ZIRCONIUM TIN TITANATE (ZST)

123 CHAPTER 6 DIELECTRIC AND CONDUCTIVITY STUDIES OF ZIRCONIUM TIN TITANATE (ZST) 6.1 INTRODUCTION We know that zirconium tin titanate ceramics are mostly used in microwave frequency applications. Previous