Synthesis, characterization and optical band gap of the Co2TiO4 nanoparticles

In this article, we report a comparative analysis of various spectroscopic studies including low‐temperature (25thinmathspacenormalKthinmathspace≤T≤300normalK) Raman spectroscopy of cobalt‐orthotitanate (Co2TiO4) and tricobalt‐tetraoxide (Co3O4), and their solid solutions false(1−xfalse) Co3O4+x of Co2TiO4 (0≤x≤1 (100 wt.%)). For all the lower and intermediate compositions, five Raman‐active modes were recognized at 689, 618, 518, 480, and 195cm−1 that are associated with A1g, Eg, and 3F2g phonon symmetries. Conversely, pure Co2TiO4 exhibits a broad spectrum of width ∼93.3cm−1 without any signatures of F2g(3) mode. At low‐temperatures (down to 25 K) the A1g and F2g peaks of both Co2TiO4 and Co3O4 shift toward the high‐frequency side with anomalies across the ferrimagnetic Néel temperature (TN ∼48±5K) and antiferromagnetic Néel temperature (TN∼ 30 ± 10 K), respectively. All the investigated samples exhibit two distinct bands at 576cm−1 (B1) and 665cm−1 (B2) in the Fourier transform infrared spectra recorded at 300±10 K, associated with the vibrational stretching of the metal–oxygen bonds of length ∼195.8 pm (B–O) and ∼185.4 pm (A–O), respectively. The intensity of these sharp bands gradually decreases as the crystal structure transforms from normal‐spinel (a=8.07 Å) to inverse‐spinel structure (a=8.45 Å). The X‐ray photoelectron spectroscopy (XPS) studies revealed that the Ti was incorporated into the octahedral B‐sites of inverse‐spinel structure of Co2TiO4. Interestingly, the XPS spectra of Co2TiO4 provide evidence of the trivalent character of Ti instead of tetravalent cationic configuration together with a weak Co3+ character at the octahedral sites. These results are discussed in terms of the binding‐energy (BE) difference between the O‐1s and Ti‐2p3/2 (Δ[O–Ti‐2p3/2] = BE(O‐1s) −BE(Ti‐2p3/2false)) and the mean chemical bond length lfalse[italicTi−Ofalse]. The peculiarities of all these results in consonance with the crystal‐structure (bond angles and bond lengths) and electron‐spin‐resonance studies are discussed in detail.

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“…Recently, Khanahmadzadeh et al. reported the synthesis of

{Co}_{2} {TiO}_{4}

nanoparticles by a sol–gel process and showed that the optical bandgap of this compound is about

1.3

eV (). Usually, above 500

{cm}^{- 1}

four significant phonon modes can be observed in polycrystalline powders and 2D thin films of

{Co}_{3} O_{4}

.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Nayak

Dasari

Joshi

et al. 2016

Physica Status Solidi (b)

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“…2. Отметим, что наши результаты по частотам фононов в монокристаллах Co 2 TiO 4 значительно отличаются от результатов, полученных на нанокристаллах [10]. Спектральная область частот 2000−15 000 cm −1 ха-рактеризуется очень интенсивным поглощением, обус-ловленным электронными переходами между 3d-под-уровнями иона Co 2+ в тетраэдрических и октаэдриче-ских позициях.…”

Section: экспериментальные результаты и их обсуждениеunclassified

“…Можно предположить, что это связано с тем, что большинство исследований было выполнено на поликристаллических и керамических об-разцах. Совсем недавно было опубликовано сообщение об oптическом исследовании наночастиц Co 2 TiO 4 , но анализа фононной и электронной структур проведено не было [10]. Можно еще добавить, что спектроскопические исследования в видимой области спектра имеют важ-ность ввиду того, что шпинель Co 2 TiO 4 является пред-ставителем группы экологически чистых (environmentfriendly) коммерческих зеленых пигментов [11].…”

Section: Introductionunclassified

Динамика решетки и электронная структура кобальт-титановой шпинели Co-=SUB=-2-=/SUB=-TiO-=SUB=-4-=/SUB=-

Просников¹,

Молчанова²,

Дубровин³

et al. 2016

Физика Твердого Тела

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Представлены результаты исследований фононных возбуждений и электронной структуры обращенной шпинели Co 2 TiO 4 , в которой ниже TC = 56 K магнитоупорядоченные ионы кобальта Co 2+ (3d 7 ) находятся в равном количестве в тетраэдрической и октаэдрической подрешетках. Исследовались монокристаллы с использованием оптических методов отражения и поглощения в широком спектральном интервале, раманов-ского рассеяния, а также метода диэлектрической спектроскопии. Изучена динамика инфракрасных и Раман-активных фононов, обнаружены особенности, связанные с наличием разупорядочения в тетраэдрических позициях. Зарегистрированные d−d-электронные переходы в области 3800 и 6300 cm −1 подтверждают координационные особенности ионов Co 2+ . Обнаружен рост диэлектрической проницаемости в области температур ниже 130 K.Работа выполнена при поддержке Российского научного фонда (проект № 16-12-10456).

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“…The material in particular has not yet been exploited in the thin film structure, as well as its physical characteristics for application in resistive memory. Some potential applications of cobalt titanate can be highlighted as: Li‐ion batteries, thermistors, fuel cells, magnetic recording, antenna materials, radiofrequency devices, photoluminescent materials, and also photocatalysts . Due to the lack of records on the RS effect in the CTO material, we have analyzed some work on its precursor materials such as Co 3 O 4 and TiO 2 , where studies on Co 3 O 4 identified bipolar RS behavior in Co 3 O 4 nanofilament, with relatively high operating voltages (≈15–40 V) for application in non‐volatile multi‐state memories .…”

Section: Introductionmentioning

confidence: 99%

“…Some potential applications of cobalt titanate can be highlighted as: Li-ion batteries, thermistors, fuel cells, magnetic recording, antenna materials, radiofrequency devices, photoluminescent materials, and also photocatalysts. [15][16][17][18] Due to the lack of records on the RS effect in the CTO material, we have analyzed some work on its precursor materials such as Co 3 O 4 and TiO 2 , where studies on Co 3 O 4 identified bipolar RS behavior in Co 3 O 4 nanofilament, with relatively high operating voltages (%15-40 V) for application in non-volatile multi-state memories. [19] Reports on resistive switching in TiO 2 thin films showed unipolar behavior and also bipolar at low voltage values.…”

Section: Introductionmentioning

confidence: 99%

Study of Filament Resistive Switching in New Pt/Co_0.2TiO_3.2/ITO Devices for Application in Non‐Volatile Memory

Góis

Valença

Machado

et al. 2018

Physica Status Solidi (a)

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In this work, the authors present a study of the resistive switching effect (RS) in Co0.2TiO3.2 (CTO) in a thin film structure Pt/CTO/ITO. The identification of a structure of low crystallinity with different deposition times is seen in the diffractograms with a certain tendency of orientation in the plane (311) of the inverted spinel of space group Fd‐3m. Electrical measurements I–V highlight the appearance of RS effect predominated by unipolar filamentary mechanism. The retention of charge in the device shows good stability and separation of HRS‐LRS states with ROFF/RON ≈106 ratio. The authors are able to demonstrate that Co0.2TiO3.2 presents promising performance for application in non‐volatile memories.

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Synthesis, characterization and optical band gap of the Co2TiO4 nanoparticles

Cited by 22 publications

References 29 publications

Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Динамика решетки и электронная структура кобальт-титановой шпинели Co-=SUB=-2-=/SUB=-TiO-=SUB=-4-=/SUB=-

Study of Filament Resistive Switching in New Pt/Co_0.2TiO_3.2/ITO Devices for Application in Non‐Volatile Memory

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Synthesis, characterization and optical band gap of the Co2TiO4 nanoparticles

Cited by 22 publications

References 29 publications

Spectroscopic studies of Co2TiO4 and Co3O4 two‐phase composites

Spectroscopic studies of Co2TiO4 and Co3O4 two‐phase composites

Динамика решетки и электронная структура кобальт-титановой шпинели Co-=SUB=-2-=/SUB=-TiO-=SUB=-4-=/SUB=-

Study of Filament Resistive Switching in New Pt/Co0.2TiO3.2/ITO Devices for Application in Non‐Volatile Memory

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Product

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Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Study of Filament Resistive Switching in New Pt/Co_0.2TiO_3.2/ITO Devices for Application in Non‐Volatile Memory