KNNS-BNW seramiklerin ZNO katkısına bağlı olarak dielektrik özelliklerinin incelenmesi = Investigation of dielectric properties of KNNS-BNW ceramics depending on zno additive

Abstract

Seramikler, elektronik uygulamalarda birçok amaçla kullanılan yaygın bir malzeme grubudur. Gelişen teknolojik faaliyetler neticesinde birçok alanda enerjiyi depolama ve dönüştürme yeteneklerinden faydalanılan piezoelektrik malzemelere ihtiyaç duyulmaktadır. Piezoelektriklerin endüstride en yaygın kullanımı geleneksel seramiklerden farklı olarak üretilen sensörler, kapasitörler (kondansatörler), aktüatörler, dönüştürücüler ve dielektrik malzemeler olarak faaliyet gösteren ileri teknoloji seramikleridir. Kurşunun elektronik özelliklere pozitif katkılar sağladığı keşfedildikten sonra kurşun-zirkonat-titanat (PZT) bileşimi endüstride kullanılan en iyi piezoelektrik malzemelerden birisi olmuştur. Ancak günümüzde yapılan çalışmalar ağır metaller içerisinde yer alan kurşunu, yüksek toksisite değerleri göstermesinden dolayı çevreye ve canlılığa zararlı etkileri olan bir tehdit unsuru olarak görmektedir. Bu sebeple kurşun içermeyen malzeme gruplarına yönelim artmış ve araştırma çalışmaları günden güne hız kazanmıştır. Bunlar içerisinde ABO3 tipi kristalleşen potasyum sodyum niyobat (KNN), potasyum stronsiyum niyobat (KSN), baryum titanat (BT) ve bizmut sodyum titanat (BNT) gibi perovskit yapılar önem kazanarak elektriksel özellikleriyle dikkat çekmiştir. Kurşun içermeyen malzeme grupları içerisinde KNN bileşimi yüksek Curie sıcaklığı (TC) ve düşük dielektrik kayıp özellikleri göstermesi sebebiyle umut vadedici bir malzemedir. KNN gibi perovskit seramiklerinin yaygın olarak kullanıldığı dielektrik malzemeler elektrik akımını taşıyan serbest elektronlara sahip değildir ancak bir elektrik alan altında polarize olarak elektrik yükünü depolamada veya kapasitansı arttırmada kullanılabilirler. Seramik malzemeler bileşimlerinde alkali ve toprak alkali bileşikler, silikatlar, alüminatlar, metal oksitler bulunduran malzeme gruplarından biridir. Bağ yapılarındaki iyonik ve kovalent durumlar, değişken kristalizasyon yapıları ve bileşim kombinasyonlarının fazla olması gibi sebepler neticesinde araştırma ve geliştirme çalışmaları devam etmektedir. Seramiklere çeşitli katkı maddeleri eklenerek kimyasal ve mekanik özellikleri değiştirilebilmekte ve bu sayede mevcut malzemelerin geliştirilmeleri veya alternatiflerinin üretilmesi sağlanmaktadır. Bu çalışmada kurşun içermeyen potasyum sodyum niyobat (KNN) tipi seramiklere farklı oranlarda ZnO katkısının [0,955(K0,52Na0,48)(Nb0,96Sb0,04)O3 – 0,045(Bi0,5Na0,5)(Zn0,5W0,5)O3] seramik sistemi (KNNS-BNZW) üzerindeki dielektrik özelliklere etkisi araştırılmıştır. Hammaddeler stokiyometrik oranlarda tartılarak ZnO katkısız KNNS-BNW ve ağırlıkça %0,05 - %0,1 ve %0,2 ZnO katkılı olacak şekilde hazırlanmıştır. Seramik tozu üretimi için toz metalurjisi yöntemi kullanılarak hammaddeler bilyeli değirmende etil alkol ortamında öğütülmüş ve kurutularak 890 ˚C sıcaklıkta 8 saat kalsinasyon yapılmıştır. İkinci kez öğütme ve kurutma aşamalarından geçirilerek elde edilen ZnO katkılı ve katkısız KNNS-BNW seramik tozları ayrı ayrı 200 MPa basınç altında tek eksenli presleme yöntemiyle şekillendirilmiştir.Geleneksel sinterleme metoduna göre 1160 ˚C sıcaklıkta 14 saat sinterlenerek üretim tamamlanmıştır. Sinterlenen seramik numunelerin yoğunluğu ölçülmüştür. Tozların ve sinterlenmiş seramik numunelerin karakterizasyonunda XRD, SEM ve EDS ile faz analizleri, mikroyapı özellikleri ve elementel analizi yapılmıştır. Yapılan XRD ölçümlerinde KNNS-BNW ve KNNS-BNZW seramiklerinin oda sıcaklığında perovskit kristal sisteminde olduğu, SEM incelemelerinde üretilen KNNS-BNW ve KNNS-BNZW seramiğinin yoğun bir yapı sergilediği görülmektedir. Dielektrik ölçümler için seramik numuneler gümüş pasta ile kaplanarak yüzeyleri iletken hale getirilmiştir. 50 Hz – 1 MHz aralığında farklı frekans ve sıcaklık değerlerine bağlı ölçümler yapılmış, kapasitans (C) ve kondüktans (G) değerleri ölçülmüştür. Ölçüm sonuçlarından dielektrik sabit (Ɛr) ve dielektrik kayıp (tanδ) değerleri hesaplanmıştır. 25 ˚C sıcaklıkta 1 kHz frekans ile yapılan ölçümde %0.05, %0.1 ve %0.2 ZnO katkılı bileşimler için Ɛr değerleri sırasıyla 1113.4, 1302.2, 856.7 ve tanδ değerleri ise 18.72, 0.55 ve 4.09 değerleridir. Seramik bileşimlerin Curie sıcaklığı (TC) yaklaşık 240 ˚C'de görülmektedir. Dielektrik ölçüm değerleri incelendiğinde üretilen KNNS-BNW esaslı seramik bileşiminin kurşun içeren seramik bileşimleri yerine kullanılabileceği görülmektedir.

Ceramics are a common group of materials used for many purposes in electronic applications. As a result of developing technological activities, piezoelectric materials that benefit from their ability to store and convert energy are needed in many areas. The most common use of piezoelectrics in industry is in advanced technology ceramics that act as sensors, capacitors, actuators, transducers and dielectric materials produced differently from traditional ceramics. After it was discovered that lead makes positive contributions to electronic properties, the lead-zirconate-titanate (PZT) composition has become one of the best piezoelectric materials used in industry. However, today's studies see lead, which is among the heavy metals, as a threat that has harmful effects on the environment and life due to its high toxicity values. For this reason, the trend towards lead-free material groups has increased and research studies have accelerated day by day. Ceramic materials are a group of materials that contain alkali and alkaline (1A and 2A groups in the periodic table) earth compounds, silicates, aluminates and metal oxides. Their research continues due to the many combinations of ionic and covalent bonds, variable crystallization structures and electron composition. By adding various additives to ceramics, their chemical and mechanical properties can be changed, thus enabling the development of existing materials or the production of alternatives. The pyroelectric effect, which is the property of creating an electric polarization in a material in response to temperature change, was studied by Cark Linnaeus and Franz Aepinus in the 18th century, and René Just Haüy and Antoine César Becquere discovered a relationship between mechanical stress and electrical charge. As a result of combining the pyroelectric feature with crystal behavior, electrical charge accumulates when pressure is applied, and the first proof of the piezoelectric effect was made by Pierre Curie and Jacques Curie in 1880, using tourmaline, quartz, topaz, sugar cane and Rochelle salt (sodium potassium tartrate tetrahydrate) crystals. Confirming the existence of the reverse effect demonstrated mathematically by Gabriel Lippmann, the Curie brothers carried out studies on measurable proof of the reversibility of electro-elasto-mechanical deformations in piezoelectric crystals. In the following period, many studies were carried out on crystal structures showing piezoelectric properties. In 1910, 20 natural crystal classes with piezoelectric properties and their piezoelectric constants were published in the literature. The piezoelectric effect was first used in sonars as ultrasonic submarine detectors during World War I. The use of piezoelectric materials in sonar systems has aroused interest thanks to the transducer by placing film-shaped quartz between two metal (steel) plates and the hydrophone that enables the detection of the converted echo. II. During World War II, research groups in the United States, Russia, and Japan discovered a class of artificial materials called ferroelectrics that had piezoelectric constants greater than those of existing natural materials. Thus, the first piezoelectricceramic discovered was barium titanate (BaTiO3). Later, lead zirconate titanate (PZT) materials were discovered and efforts to improve their properties began. As a result of the increasing studies on the harmful effects of lead, many piezoelectric ceramic classes with different layer structures have emerged. Among these, perovskite structures such as potassium-sodium-niobate (KNN), potassium-strontium niobate (KSN), barium-titanate (BT) and bismuth-sodium-titanate (BNT), which crystallize into the ABO3 type and show good electrical properties, have gained importance. Among the lead-free material groups, KNN composition is a promising material due to its high Curie temperature (TC) and low dielectric loss properties. Ceramics such as bismuth titanate (Bi4Ti3O12), which have a bismuth-layer structure, are important with their low piezoelectric constant and high Curie Temperature. Additionally, high anisotropy occurs in the coupling factor. Thanks to these features, they are used in high TC sensors, resonators and filtering. Tungsten bronze structured materials such as Sr2-xCaxNaNb5O15 and SrxBa1-xNb2O6 are used in electrooptical, photorefractive and pyroelectric applications, microwave and high power laser applications. BaTiO3 and (Na0.5K0.5)NbO3 (KNN) type perovskite structured ceramics with ABO3 type crystal system are good ferroelectric materials. It is used in high power applications and actuators. Anions and cations in the A- and B- regions in the ABO3 crystal structure are important for the change of crystal symmetries and phase transformations. Although dielectric materials such as KNN, where perovskite ceramics are commonly used, do not have free electrons that can carry electric current, they have the property of being polarized under an electric field. They flow. In this way, it is used to store electrical charge or increase capacitance. Different materials are used in capacitors because they show various electrical properties. Sodium and potassium, which are volatile by nature, cause some difficulties in the production of KNN. Studies have been carried out on the condensation of the KNN system for many years. Some of those; pressure sintering method, spark plasma sintering method and the use of various additions. Good electrical properties have been achieved by obtaining high densities with pressure sintering or spark plasma sintering methods, but they are not preferred because they are more expensive than traditional sintering and require detailed research and optimization. Some negative properties of ceramics can be changed with the help of additives added to the composition. In this study, different amounts of ZnO addition to lead-free potassium sodium niobate (KNN) type ceramics [0.955(K0.52Na0.48)(Nb0.96Sb0.04)O3 – 0.045(Bi0.5Na0.5)(Zn0.5W0.5)O3], its effect on the dielectric properties on the ceramic system (KNNS-BNZW) was investigated. Raw materials were weighed in stoichiometric proportions and prepared as pure KNNS-BNW and 0.05% - 0.1% and 0.2% ZnO added by weight. Using the powder metallurgy method to produce ceramic powder, the raw materials were ground in a ball mill in ethyl alcohol environment, dried and calcined at 890 ˚C for 8 hours. KNNS-BNW ceramic powders with and without ZnO added, which were obtained by going through the second grinding and drying stages, were shaped separately by the uniaxial pressing method under 200 MPa pressure. According to the traditional sintering method, production was completed by sintering at 1160 ˚C for 14 hours. The density of the sintered ceramic samples was measured. In the characterization of powders and sintered ceramic samples, phase analysis, microstructural properties and elemental analysis were performed by XRD, SEM and EDS. In XRD measurements, it is seen that KNNS-BNW and KNNS-BNZW ceramics are in the perovskite crystal system at room temperature, and in SEMexaminations, the produced KNN ceramics exhibit a dense structure. For dielectric measurements, ceramic samples were coated with silver paste and their surfaces were made conductive. Measurements were made based on different frequencies and temperature values in the range of 50 Hz - 1 MHz, and capacitance (C) and conductance (G) values were measured. Dielectric constant (Ɛr) and dielectric loss (tanδ) values were calculated from the measurement results. In the measurement made with 1 kHz frequency at 25 ˚C temperature, Ɛr values for 0.05%, 0.1% and 0.2% ZnO doped compounds are 1113.4, 1302.2, 856.7 and tanδ values are 18.72, 0.55 and 4.09, respectively. Ceramic compositions show a high Curie temperature (TC) at approximately 240 ˚C. When the dielectric measurement values are examined, it is seen that KNNS-BNW-based ceramic composition produced can be used instead of ceramic compositions containing lead.