• refractive parameters (indexes of refraction, birefringence, transmission and absorption spectra, piezooptic properties) of mechanically free and uniaxially stressed crystals, posessing a set of phase transitions;
• crystal optics of ferroics;
• phase transformations in crystalline dielectrics;
• Physics of incommensurate phases;
• low temperature physics.

Professor Vasyl Stadnyk is a scientific supervisor of 12 thesis for the Candidate of Physical and Mathematical Sciences and Ph.D. thesis:

1. Tuzyak M. R. “Optic-spectral characteristics of uniaxially stressed ammonium sulfate crystals” (Lviv, 2009);
2. Kohut Z. O. “The electron polarizability of uniaxially stressed K₂ZnCl₄ crystals with the incommensurate phase” (Lviv, 2012);
3. Kiryk Yu. I. “The refractive parameters of uniaxially stressed doped TGS-group crystals” (Lviv, 2013);
4. Kashuba O. Z. “Effect of uniaxial pressures on the optoelectronic properties of ABSO₄-type crystals” (Lviv, 2015);
5. Rudysh M. Ya. “Electronic and optical properties of lithium ammonium sulfate crystals under uniaxial stress” (Lviv, 2018);
6. Shchepanskyi P. A. “Band structure peculiarities and optical characteristics of  the ABSO₄-group crystals (where A, B = Li, Na, K, NH₄ ) with an isotropic point” (Lviv, 2019);
7. Matviiv R. B. “The influence of impurities on the optical-electronic parameters of dielectric crystals of sulfates group” (Lviv, 2021);
8. Horon B. I. “Optical and electronic parameters of fluoroberyllate group crystals” (Lviv, 2024);
9. Pryshko I. A. “Thermo-optical and band-energy parameters of Rb₂SO₄ crystals under the action of external factors” (Lviv, 2025);
10. Shtuka O.V. “Concentration dependences of dielectric parameters of A₂BX₄-group crystals”;
11. Vatamaniuk R.I. “Analysis of the parameters of acousto-optic interaction in crystalline dielectrics”;
12. Markevych O.A. “Determination of elasto-optic parameters of chlorozincate group crystals”.

Professor Vasyl Stadnyk was a scientific consultant of the thesis for the Doctor of Physical and Mathematical Sciences:

Brezvin R. S. “The influence of isomorphic substitution and external fields on the optoelectronic parameters of the sulfate and chlorozincate groups ferrics” (Lviv, 2020).

Articles:

1. Andriyevsky B. Electronic band structure and influence of uniaxial stresses on the properties of K₂SO₄ crystals: ab initio study / B. Andriyevsky, M. Jaskólski, V. Y. Stadnyk  [et al.]  // Computatioanal Materials Science. – 2013. – Vol. 79. – P. 442–447.
2. Stadnyk V. Y. Piezo-optic properties of K₂SO₄ crystals / V. Y. Stadnyk, O. Z. Kashuba, R. S. Brezvin [et al.] // Crystallography Reports. – 2014. – Vol. 59, No. 1. – Р. 101–104.
3. Rudysh М. Ya. Energy band structure of LiNH₄SO₄ crystals / М. Ya. Rudysh, V. Yo. Stadnyk, R. S. Brezvin, P. А. Shchepanskyi // Physics of the Solid State. – 2015. – Vol. 57, No. 1. – P. 53–58.
4. Кurlyak V. Yu. Piezo-optical properties of incommensurately modulated Rb₂ZnCl₄ crystals /  V. Yu. Кurlyak,   V. Y. Stadnyk, O. V. Bovgira, V. B. Stakhura // Optics and Spectroscopy. – 2015. – Vol. 118, № 4. – P. 547–551.
5. Stadnyk V. Yo. Piezo-optic properties of LiNH₄SO₄  crystals / V. Yo. Stadnyk, R. S. Brezvin, М. Ya. Rudish  [et al.] // Crystallography Reports. – 2015. – Vol. 60, № 3. – P. 388–392.
6. Кurlyak V. Yu. Temperature-pressure phase diagram for Rb₂ZnCl₄ crystals / V. Yu. Кurlyak, V. Yo. Stadnyk, V. Stachura // Journal of Applied Spectroscopy. – 2015. – Vol. 82, № 2. – P. 228–233.
7. Andriyevsky B. Influence of uniaxial stresses on electronic and optical properties of β-K₂SO₄ crystal / B.  Andriyevsky, M.  Jaskólski, V. Y.  Stadnyk [et al.] // Materials Science-Poland. – 2015. – Vol. 33,   № 1. – P. 11–17.
8. Andriyevsky B. Electronic band structure and optical properties of ferroelectric TGS, TGSe and TGFB crystals / B. Andriyevsky, V. Yu. Kurlyak, V. Yo. Stadnyk [et al.] // Materials Chemistry and Physics. – 2015. – Vol. 162.  – P. 787–793.
9. Kurlyak V. Yu. Birefringence of mechanically stressed Rb₂ZnCl₄ crystals / V. Yu. Kurlyak, V. Yo. Stadnyk, V. B. Stakhura, Z. O. Kohut // Crystallography Reports. – 2015. – Vol. 60, № 6. – P. 929–934.
10. Kurlyak V. Yu. Optical properties of D-serine doped TGS crystals for pyroelectric sensors / V. Yu. Kurlyak, V. Yo. Stadnyk, B. V. Andriyevsky [et al.] // Materials Science-Poland. – 2015. – Vol. 33, № 4. – P. 692–698.
11. Kurlyak V. Yu. The temperature changes of refractive indices and thickness of doped triglycine sulfate crystals / V. Yu. Kurlyak, V. Y. Stadnyk, V. M. Gaba [et al.]  // Journal of Applied Spectroscopy. – 2016. – Vol. 83, № 3. – P. 472–477.
12. Andriyevsky B. Electronic band structure and related properties of Rb₂ZnCl₄ crystals at different hydrostatic pressures / B. Andriyevsky, V. Kurlyak, V. Stadnyk [et al.] // Computational Materials Scince. – 2016. – Vol. 111. – P. 257–262.
13. Rudysh M. Ya. Ionicity and birefringence of α-LiNH₄SO₄ crystals: ab initio DFT study, X-ray spectroscopy measurements / M. Ya. Rudysh, M. G. Brik, O. Y. Khyzhun [ V. Yo. Stadnyk and et al.] // Royal Society of Chemistry Advances.– 2017. – Vol. 7. – P. 6889–6901.
14. Stadnyk V. Y. Rerfactometry of Rb₂ZnCl₄ crystals under uniaxial pressure / V. Y. Stadnyk, V. B. Stakhura, B. V. Аndrievskii // Оptics and Spectroscopy. – 2017. – Vol. 122, № 6. – P. 995–1001.
15. Shchepanskyi P. A. Structure and optical anisotropy of K_1.75(NH₄)_0.25SO₄ solid solution / P. A. Shchepanskyi, O. S. Kushnir, V. Yo. Stadnyk [et al.] // Ukr. Journ. Phys. Optics. – 2017.– Vol. 18, № 4. – P. 187–196.
16. Rudysh M. Ya. Ab initio calculations of the electronic structure and specific optical features of β-LiNH₄SO₄ single crystals / M. Ya. Rudysh, M. G. Brik, V. Yo. Stadnyk [et al.] // Physica B: Physics of Condensed Matter. – 2018. – Vol. 528. – P. 37–46.
17. Shchepanskyi P. A. The influence of partial isomorphic substitution on electronic and optical parameters of ABSO₄ group crystals / P. A. Shchepanskyi,  M. Gaba, V.  Yo. Stadnyk [et al.] // Acta Phys. Pol. A.  – 2018. – Vol. 138, No 4. – P. 819–823.
18. Rudysh M. Ya. Raman scattering spectra of β-LiNH₄SO₄ crystals / M. Ya. Rudysh, A. I. Kashuba, V. Yo. Stadnyk [et al.] // Journal of Applied Spectroscopy – 2019. – Vol. 85, No. 6. – P. 1022–1028.
19. Stadnyk V. Yo. On isotropic points in potassium ammonium sulphate / V. Yo. Stadnyk, P. A. Shchepanskyi, R. S. Brezvin [et al.] // Crystals Crystallography Reports. – 2019. – Vol. 64, No. 5. –  Р. 787–795.
20. Stadnyk V. Y. Photoelastic properties of potassium sulfate crystals / V. Y. Stadnyk, R. B. Matviiv, P. A. Shchepanskii, M. Ya. Rudysh, and Z. A. Kogut. // Physics of the Solid State. – 2019. – Vol. 61, No. 11. – P. 2130–2133.
21. Stadnyk V. Yo. Pressure-induced changes in parameters of the indicatrix of lithium sodium sulfate crystals / V. Yo. Stadnyk, Р. A. Shchepanskyi, R. S. Brezvin [et al.] //  Optics and Spectroscopy. – 2019. – Vol. 127. – P. 1023–1027.
22. Stadnyk V. Yo. Refractive parameters and band energy structure of K₂SO₄ crystals doped with copper / V. Yo. Stadnyk, R. B. Matviiv, M. Ya. Rudysh [et al.] // Journal of Applied Spectroscopy. – 2020. – Vol. 87. – P. 143–149.
23. Rudysh M. Ya. Specific features of refractive, piezo-optic and nonlinear optical dispersions of β-LiNH₄SO₄ single crystals / M. Ya. Rudysh,  V. Yo. Stadnyk, P. A. Shchepanskyi [et al.] // Physica B: Condensed Matter. – 2020 – Vol. 18. – P. 411919.
24. Stadnyk V. Yo. On isotropic points in K₂SO₄ impurity crystals / V. Yo. Stadnyk, R. B. Matviiv, R. S. Brezvin, P. A. Shchepanskyi, Z. A. Kogut // Optics and spectroscopy. – 2021. – No 129. – P. 227–233.
25. Matviiv R. B. Structure, refractive and electronic properties of K₂SO₄:Cu²⁺ (3%) crystals / R. B. Matviiv, M. Ya. Rudysh, V. Yo. Stadnyk, A. O. Fedorchuk, P. A. Shchepanskyi, R. S. Brezvin, O. Y. Khyzhun // Current Applied Physics. – 2021. – Vol. 21. – P. 80–88.
26. Matviiv R. Thermal and refractive properties of doped K₂SO₄ crystals in the region of the phase transition / R. Matviiv, V. Stadnyk, R. Brezvin, P. Shchepanskyi, M. Rudysh, O. Kostetskyi // Journal of Physical Studies. – 2021. – Vol. 25, No. 2. – P. 2703.
27. Rudysh M. Ya.  Structure, optical, and electronic properties of sodium ammonium sulfate dehydrate crystal / M. Ya. Rudysh,  P. A. Shchepanskyi, O. Y. Khyzhun,  A. K. Sinelnichenko,  R. S. Brezvin,  V.  Yo. Stadnyk,  A. O. Fedorchuk  // Optical Materials. – 2025. – Vol. 158.  – P.  116501.
28. Rudysh M. Ya.  Characterization of electronic structure and luminescence spectra of the K₂SO₄ crystal / M. Ya. Rudysh, R. S. Brezvin, O. Yu. Khyzhun, М. Piasecki,  N. M. Melnykova, V. Yo. Stadnyk, P. А. Shchepanskyi, A. Kotlov // Applied Physics A Materials Science and Processing. – 2025. – 131(8). – P.  604.
29. Ftomyn N. Investigation of optical anisotropy in Rb₂SO₄ crystals by high-accuracy polarimetry / N. Ftomyn, P. Shchepanskyi, V. Vyshnevskyi, I. Pryshko, V. Stadnyk, R. Brezvin, O. Onufriv, Y. Shopa // Jour.Phys. St. – 2025. – V. 29, No. 3 – P. 3703(7 p.)

Pathents:

1. Пат. 128162 Україна на корисну модель, МПК G01N 21/39 (2006.01). Пристрій для дослідження оптичної якості монокристала / Стадник В. Й., Габа В. М., Сугак Д. Ю., Брезвін Р. С., Рудиш М. Я., Щепанський  П. А. ; заявник Львівський національний університет імені Івана Франка, власники Львівський національний університет  імені Івана Франка, Національний університет “Львівська політехніка”. –  №u201801973 ; заявл. 26.02.2018 ; опубл. 10.09.2018, бюл. № 17.
2. Пат. 139890 Україна (на корисну модель), МПК:G01L 1/24 (2006.01). Пристрій для вимірювання одновісного механічного тиску / Стадник В. Й., Рудиш М. Я., Щепанський П. А., Матвіїв Р. Б., Габа    В. М., Когут З. О., Брезвін Р. С. ; заявники і власники Львівський національний університет імені Івана Франка, Національний університет “Львівська політехніка”. – № u201907532 ; заявл. 05.07.2019 ; опубл. 27.01.2020, бюл. № 2/2020.
3. Пат. 140611 Україна (на корисну модель), МПК (2006): G01K 11/00, G01K 11/32 (2006.01). Пристрій для оптичного вимірювання температури / Стадник В. Й., Габа В. М., Рудиш М. Я., Щепанський П. А., Матвіїв Р. Б., Брезвін Р. С., Петрович І. В. ; заявники і власники Львівський національний університет імені Івана Франка, Національний університет “Львівська політехніка”. – № u201907533; заявл. 05.07.2019 ; опубл. 10.03.2020, бюл. № 5/2020.
4. Патент 159901 (13) U (51) Україна (на корисну модель), МПК (2006): G02F 1/11 (2006.01). Акустооптичний модулятор/ Стадник В. Й., Брезвін Р. С., Пришко І. А., Щепанський П. А., Вишневський В. В.;  заявник і власник Львівський національний університет імені Івана Франка. – № u202406019; заявл. 17.12.2024 ; опубл. 16.07.2025, бюл. № 29.

In 1985 Vasyl Stadnyk graduated from the Faculty of Physics of Ivan Franko State University of Lviv with honors. He received full higher education on a specialty “Optical and opto-electronic systems” and got a qualification of an engineer-optician-researcher.

From 1985 till 1986 he worked as an engineer at the Research and Development Department of the Ivan Franko State University of Lviv.

From 1986 till 1987 he was an engineer of the Department of Experimental Physics.

From 1987 till 1990 he was a post-graduate student on the Department of Experimental Physics of Ivan Franko State University of Lviv.

In 1990 Vasyl Stadnyk defended his Ph.D. thesis named “Electron polarization of А₂ВХ₄ group crystals with incommensurate phases“. He had been awarded a candidate degree of sciences in physics and mathematics, specialty – solid state physics.

From 1990 till 1991 he worked as a junior researcher and from 1991 till 1992 as a senior researcher at the Research and Development Department of Ivan Franko State University of Lviv.

From1992 til 1999 Vasyl Stadnyk worked as an assistant, during next 1999–2007 years – a docent of the Department of Experimental Physics of Ivan Franko State University of Lviv (since October 11, 1999, Ivan Franko National University of Lviv).

In 1999 he was awarded the academic status of an associate professor of the Department of Experimental Physics.

In 2006 he defended his thesis for a doctor degree named “Baric changes of the refractive parameters of dielectric crystals“. He was awarded the scientific degree of a doctor of  sciences in physics and mathematics, specialty –  physics of semiconductors and insulators.

From 2007 till 2008 Vasyl Stadnyk worked as a docent, from 2008 till 2016 – a professor of the Department of Solid State Physics of Ivan Franko National University of Lviv.

In 2011 he was awarded the the academic status of a professor of the Department of Solid State Physics.

Since May 2016 he is a chairperson of the Department of General Physics of the Ivan Franko National University of Lviv.

He was a scientific co-supervisor the economic contractual theme named “Synthesis of a new class of crystalline materials of А₂ВХ₄ group and study of the prospects of their effective application in electromagnetic radiation controlling devices” in 2017 and 2018 years.

Vasyl Stadnyk was a scientific supervisor of the State budget theme Fz-53F named “New materials for functional electronics on the basis of semiconductor and dielectric crystals of А₄ВХ₆ and А₂ВХ₄ groups” (2017-2019 years).

He was a scientific supervisor of the State budget theme Fz-08F named “Transformation of the optic-electronic parameters and structure of new crystalline materials for sensor devices and optoelectronics” (2020-2022 years) and Grant of the National Research Fund of Ukraine 2020.02/0211 “Experimental and theoretical study and prediction of the photoelastic properties of crystalline materials for devices of electromagnetic radiation control”.

Currently Professor Vasyl Stadnyk is a scientific supervisor of the State budget theme Fz-01F named “New broadband materials for detecting and controlling electromagnetic radiation in dual-purpose devices“ (01.01.2024 – 31.12.2026).

He is an author of 382 scientific publications and 6 utility models of Ukraine.

Vasyl Stadnyk is a supervisor of 12 thesis (9 thesis of them were defended). Currently he supervises the research work of 3 Postgraduate Students of the Department of General Physics. Professor Vasyl Stadnyk was a scientific consultant of the thesis for the Doctor of Physical and Mathematical Sciences.

He is the guarantor of the bachelor’s degree program at Ivan Franko National University of Lviv, subject specialty 014.08 “Secondary Education (Physics)”.

Professor Vasyl Stadnyk was awarded the Honorary Title “Honored Professor of Ivan Franko National University of Lviv” on September 29, 2021.

Teaching and methodological work of Vasyl Stadnyk includes 4 monographs, 4 tutorials and 3 methodical materials.

Professor V. Yo. Stadnyk was a scientific co-supervisor and a scientific supervisor of the themes and the grant of the National Research Fund of Ukraine:

• the Economic contractual theme named “Synthesis of a new class of crystalline materials of А₂ВХ₄ group and study of the prospects of their effective application in electromagnetic radiation controlling devices” in 2017 and 2018 years;
• the State budget theme Fz-53F named “New materials for functional electronics on the basis of semiconductor and dielectric crystals of А₄ВХ₆ and А₂ВХ₄ groups” (2017-2019 years);
• the State budget theme Fz-08F named “Transformation of the optic-electronic parameters and structure of new crystalline materials for sensor devices and optoelectronics” (2020-2022 years). Aim of the work: Elucidation of optic-electronic and band-energy parameters of ferroics of ABSO₄ (including substitutional solid solutions and crystals incorporated by transition metal impurities) and A₄BX₆ structural types and the influence of external fields on them for possible use of the crystals as active elements of functional electronics devices.
• the Grant of the National Research Fund of Ukraine 2020.02/0211 “Experimental and theoretical study and prediction of the photoelastic properties of crystalline materials for devices of electromagnetic radiation control”. Aim of the work: Development of a methodology for accurate study and prediction of refractive characteristics and creation of a database of the firstly synthesized crystalline materials of the A₂BX₄ group for their effective use in optoelectronic devices, including acoustic-optical cells.

Currently Professor Vasyl Stadnyk is a scientific supervisor of the State budget theme Fz-01F named “New broadband materials for detecting and controlling electromagnetic radiation in dual-purpose devices” (01.01.2024 – 31.12.2026). Aim of the work: Synthesis, experimental-theoretical research and elucidation of the mechanism of influence of external factors, cation-anion isomorphic substitutions, as well as admixture with atoms of transition metals on the temperature-spectral changes of the optical-electronic parameters of the crystals of the А₂ВХ₄ group; development of recommendations regarding the possible practical application of the studied materials as active light-sensitive elements in electromagnetic radiation control devices and sensors.

2024:

The dielectric permittivity along the polar axis of the (NH₄)₂BeF₄ crystal was investigated by an automated capacitive method in the paraelectric, incommensurate, and commensurate ferroelectric phases. It was found that the dielectric permittivity of the (NH₄)₂BeF₄ crystal is not affected by the transition from the paraelectric to the incommensurate phase in T_i, and only a weak peak appears at the point of the incommensurate–ferroelectric phase transition T_C. The experimental results for the incommensurate phase of the AFB were compared with the data of four phenomenological theories: the Curie–Weiss law, the generalized Curie–Weiss law, the Levanyuk and Sannikov (LS) and Prelovšek, Levstik and Filipič (PLF) models. It is found that the PLF model provides results very similar to those of the inverse power laws given by the Curie–Weiss and generalized Curie–Weiss formulas. Analysis of experimental data shows that the temperature slopes of both the inverse permittivity with the dielectric background subtracted and the permittivity represented on a double logarithmic scale vary continuously with temperature. The temperature dependence of the permittivity within the Levanyuk–Sannikov model is governed by a combination of linear terms with respect to temperature, and the peak at the PT point at temperature T_C is ‘damped’ by the temperature-dependent terms. This mathematical procedure provides the necessary change in the slope of the curves ε(T) and so appropriately describes the experimental data.

2025:

The dispersion dependences of birefringence of a mechanically free and uniaxially clamped Rb₂SO₄ crystal at room temperature were investigated. It was found that the crystal has an insignificant normal dispersion d(Δn_x)/dλ < = 0, and uniaxial compressions σ_m do not change the character, but only the magnitude of the slope of the curves Δn_і(λ). Uniaxial loads shift the position of the optical isotropic point both in the short-wavelength (σ_z ) and long-wavelength regions of the spectrum (σ_y). The spectral dependences of the combined piezocoefficients  were calculated and it was found that they have a negligible dispersion dependence, and the piezocoefficients  and  in the vicinity of the optical isotropic point at a light wavelength l = 490 nm are equal to each other. Large single crystals of NaNH₄SO₄ × 2H₂O were grown by slow solvent evaporation, measuring approximately 20 × 19 × 16 mm, were transparent and colourless, and had good optical quality, as verified by conoscopy and extinction under a polarizing microscope. The single-phase nature of the samples was confirmed by X-ray diffraction and its crystal structure was clarified. It was found that NaNH₄SO₄ × 2H₂O belongs to the orthorhombic space group P2₁2₁2₁ (Z = 4).

Professor Vasyl Stadnyk was awarded the Honorary Title “Honored Professor of Ivan Franko National University of Lviv” on September 29, 2021.

Monographs:

1. Стадник В. Й. Рефрактометрія діелектричних кристалів з несумірними фазами : монографія / В. Й. Стадник, В. М. Габа. – Львів : Ліга-Прес, 2010. – 352 с.
2. Стадник В. Й. Електронна поляризовність фероїків : монографія / В. Й. Стадник, М. О. Романюк,     Р. С. Брезвін. – Львів : ЛНУ імені Івана Франка, 2013. – 306 с.
3. Брезвін Р. С. Оптико-електронні параметри кристалів групи сульфатів та цинкатів : монографія / Р. С. Брезвін, В. М. Габа, М. О. Романюк, В. Й. Стадник. – Львів : Ліга-Прес, 2018. – 244 с.
4. Рудиш М. Я. Зонна структура та рефрактивні параметри кристалів з ізотропною точкою : монографія / М. Я. Рудиш, П. А. Щепанський, В. Й. Стадник, Р. С. Брезвін. – Львів: ЛНУ імені Івана Франка, 2022. – 264 с.

Tutorials:

1. Стадник В. Й. Оптика, елементи атомної та ядерної фізики : навч. посібник [для студ. вищ. навч. закл. (гриф МОН України)] / В. Й. Стадник. – Львів : ВЦ ЛНУ імені Івана Франка, 2008. – 360 с.
2. Франів А. Фізика низьких температур : навч. посібник / А. Франів, В. Стадник, В. Курляк. – Львів : ЛНУ імені Івана Франка, 2018. – 362 с.
3. Антоняк О. Т. Загальна фізика : підґрунтя оптики : навч. посібник / О. Т. Антоняк, В. Й. Стадник. – Львів : ЛНУ імені Івана Франка, 2019. – 216 с.
4. Стадник В. Й. Фізика діелектриків : навч. посібник / В. Й. Стадник, В. Б. Капустяник. – Львів : ЛНУ імені Івана Франка, 2020. – 336 с.

Methodical materials:

1. Стадник В. Й. Методичні вказівки до лабораторних робіт зі спецкурсу “Кристалооптика і кристалофізика” для студентів фізичного факультету (Ч. ІІІ) / В. Й. Стадник, М. О. Романюк, Б. В. Андрієвський, В. Ю. Курляк. – Львів, 1988. – 36 с.
2. Стадник В. Й. Методичні рекомендації до виконання лабораторних робіт зі спецкурсу “Лазерна метрологія” для студентів фізичного факультету / В. Й. Стадник, М. О. Романюк, Б. В. Андрієвський, В. Ю. Курляк. – Львів, 2001. – 48 с.
3. Стадник В. Й. Методичні вказівки до лабораторних робіт зі спецкурсу “Кристалооптика і кристалофізика” для студентів фізичного факультет (Ч. ІV)./ В. Й. Стадник, В. Ю. Курляк, М. О. Романюк, Б. В. Андрієвський, Л. Т. Карплюк. – Львів, 2003. – 72 с.

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